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PHOTOSCOPY 

(Skiascopy    or    Retinoscopy) 


BY 


MARK  D.  STEVENSON,  M.D. 

OPHTHALMIC  SURGEON  TO  THE  AKRON  CITY  HOSPITAL;  OCULIST  TO  THE 

CHILDREN'S  HOME,  AKRON,  OHIO;  OPHTHALMOLOGIST  TO 

THE  WHITE  HOSPITAL,  RAVENNA,  OHIO 


ILLUSTRATED 


PHILADELPHIA   AND   LONDON 

W.  B.  SAUNDERS   COMPANY 

1906 


Copyright,   1906.  by  W.  B.  Saunders  Company 


PRINTED    IX    PHILADELPHIA 


wu) 


PREFACE 


PROBABLY  every  ophthalmologist  is  more  or  less  skilled 
in  the  practical  application  of  this  objective  test,  but 
without  a  thorough  understanding  of  its  simple  optical 
principles,  the  best  results  cannot  be  obtained.  This 
book  not  only  attempts  to  explain  clearly  its  use,  but  also 
to  elucidate  the  reasons  of  the  various  phenomena  ob- 
served. In  the  diagrams  light  rays  are  represented  as 
passing  from  one  point  of  an  illuminated  area,  instead 
of  from  two  or  more  points,  for  the  sake  of  clearness. 
Discussion  of  some  minor  details  of  little  or  no  prac- 
tical significance  has  either  been  very  brief  or  entirely 
omitted,  fearing  that  it  might  only  confuse  the  student. 
The  name  of  the  test  is  considered  in  Chapter  V. 

The  writer  does  not  presume  to  detract  from  the 
teachings  or  writings  of  others,  and  has  fully  availed 
himself  of  material  wherever  found,  especially  acknowl- 
edging his  obligations  to  the  excellent  works  of  Dr. 
Edward  Jackson  and  Dr.  James  Thorington.  He 
also  takes  sincere  pleasure  in  acknowledging  the  ex- 
tremely kind  and  ready  assistance  of  his  brother,  Dr. 
D.  W.  Stevenson  of  Richmond,  Indiana,  his  asso- 
ciate, Dr.  E.  L.  Mather,  and  his  assistant,  Dr.  E.  M. 
Weaver. 

M.  D.  S. 

AKROX,  OHIO,  August,  1906. 


CONTENTS 


CHAPTER  I. 

DEFINITION. — VALUE. — SUGGESTIONS  FOR  BEGINNERS. — NECESSARY 
INSTRUMENTS 17 

CHAPTER   II. 

UNDERLYING  PRINCIPLES. — PRINCIPLES  OF  PHOTOSCOPY. — BRILLIANCY 
OF  THE  LIGHT  IN  THE  PUPIL. — DEGREE  AND  RATE  OF  MOVEMENT. 
— MATHEMATICAL  POINT  OF  REVERSAL. — EXPERIMENTS  AND  OB- 
SERVATIONS   28 

CHAPTER  III. 

PRACTICAL  APPLICATION  OF  THE  TEST  WITH  THE  PLANE  MIRROR. — 
EMMETROPIA. — HYPERMETROPIA. — MYOPIA. — REGULAR  ASTIGMA- 
TISM.— MIXED  ASTIGMATISM. — IRREGULAR  ASTIGMATISM. — POSI- 
TIVE ABERRATION. — NEGATIVE  ABERRATION. — CONICAL  CORNEA. 
—  CONICAL  ASTIGMATISM. — SCISSORS  APPEARANCE. — ACCOMMO- 
DATION.— SUMMARY 51 

CHAPTER  IV. 

GENERAL  CONSIDERATIONS. — CYCLOPLEGICS. — CONCAVE  MIRROR. — 
AIDS  TO  ACCURACY. — AUTO-PHOTOSCOPY. — RELATIVE  ADVANTAGES 
OF  PLANE  AND  CONCAVE  MIRRORS 81 

CHAPTER  V. 
HISTORY. — NAME. — OTHER  INSTRUMENTS 103 


BIBLIOGRAPHY 113 

INDEX..     123 


PHOTOSCOPY. 


CHAPTER  I. 

DEFINITION.— VALUE.  — SUGGESTIONS    FOR    BEGIN- 
NERS.^NECESSARY  INSTRUMENTS. 

Definition. — Photoscopy  is  the  method  of  estima- 
ting the  refractive  error  of  an  eye,  by  reflecting  light 
into  it  by  a  plane  or  concave  mirror,  while  rotating  or 
tilting  the  mirror,  and  observing  the  size,  shape,  bril- 
liancy, direction,  and  rate  of  movement  of  an  area 
(image)  of  light  apparently  in  the  observed  eye. 

This  light  area  is  a  more  or  less  magnified  and  dis- 
tinct image  of  the  light  illumination  on  the  retina,  and  is 
formed  by  those  rays  of  light  from  this  bright  retinal 
illumination  which  pass  out  of  the  observed  eye  and 
enter  the  examiner's  eye. 

Unless  the  examiner  is  located  at  the  anterior  focal 
point  of  an  eye  (that  point  in  front  of  an  eye  where  rays 
of  light  passing  out  of  it  focus,  or  are  focused  by  lenses), 
many  rays  of  light  pass  out  of  the  patient's  pupil  that 
do  not  pass  into  his.  The  area  of  the  pupil  of  the  ob- 
served eye  through  which  these  rays  pass  appears  slightly 
dark,  and  is  said  to  be  in  a  shadow.  The  light  rays 
passing  through  this  dark  portion  of  the  observed  pupil, 
which  surrounds  the  bright  central  area  or  image,  to 
the  examiner's  eye,  are  reflected  from  the  dimly  illu- 

2  I? 


1 8  PHOTOSCOPY. 

minated  portion  of  the  retina.  All  other  rays  which 
pass  from  the  observed  to  the  observer's  pupil,  forming 
the  central  image,  are  reflected  from  the  bright  illu- 
minated portion  of  the  patient's  retina. 

The  central  light  area,  sometimes  called  spot  or  image, 
is  always  projected  (appears  to  be)  in  the  direction  of 
that  area  in  the  pupil  of  the  observed  eye  through 
which  light  from  the  retinal  illumination  passes  to  the 
examiner's  eye. 

The  area  or  image  of  light  does  not  any  more  resemble 
its  source — the  true  light  illumination  on  the  retina — in 
size,  shape,  or  location,  than  the  image  of  an  object  re- 
sembles the  object  when  seen  through  a  powerful  con- 
vex lens.  It  may  be  of  different  size  or  shape,  and  be 
situated  immediately  in  front,  above,  below,  or  on  one 
side  of  it,  depending  on  whether  it  is  viewed  through 
the  middle,  upper,  lower,  or  lateral  portion  of  the  lens. 

Value  of  Photoscopy.— The  value  of  photoscopy 
is  based  upon  the  following  facts: 

1.  The  character  of  the  refractive  error,  if  any  be 
present — e.  £.,  myopia,   hypermetropia,  astigmatism- 
is  quickly  diagnosticated. 

2.  Even  those  who  are  not  expert  in  this  method  can 
obtain  approximate  results  more  quickly  than  by  any 
other. 

3.  It  saves  much  time. 

4.  It  requires  no  expensive  or  complex  apparatus. 

5.  No  questions  need  be  asked  of  the  patient. 

6.  It  is  an  objective  test,  practically  made  without 
the  patient's  cooperation,  and  wholly  independent  of  his 
age,  intelligence,  visual  acuity,  or  indifference. 

7.  It  is  by  far  the  most  accurate  objective  test  of  the 
present   day.     By   an   expert   operator   nearly   always 


SUGGESTIONS    FOR    BEGINNERS.  IQ 

fair,  and  very  frequently  absolutely  correct,  results  are 
obtained. 

8.  It  inspires  the  confidence  of  the  patient,  and  dis- 
pels the  anxiety  of  examiner  and  patient,  when  the  latter 
sees  satisfactorily  through  the  properly  adjusted  cor- 
recting lenses. 

9.  It  gives  a  good  idea  of  the  refraction  through  partic- 
ular areas  of  the  pupil,  which  is  often  very  important. 
In  some  cases  it  may  be  a  help  as  to  proposed  operative 
measures, — e.  g.,  the  best  position  for  an  optical  iridec- 
tomy. 

10.  By  it  we  can  determine  objectively  the  amount 
of  the  accommodation,  the  knowledge  of  which  is  of 
special  service  in   examining  children, — e.  g.,  in  post- 
diphtheritic  paralysis  of  the  ciliary  muscle. 

11.  It  is  indispensable  in  examining  young  children, 
the  feeble  minded,  and  the  illiterate;    also  in  nystag- 
mus, amblyopia,  and  aphakia.     In  examining  stupid 
young  or  old  people  who  insist  upon  describing  every- 
thing they  see,  and  some  things  they  do  not,  or  who  have 
a  fondness  for  reading  the  test  types  over  and  over 
again  from  the  top  to  the  bottom,  this  test  is  a  friend  in 
time  of  need. 

12.  It  is  simple;     any  one  with  ordinary  skill  and 
qualifications  can  quickly  learn  its  principles  and  cor- 
rect application. 

Suggestions  for  Beginners. — i.  Be  patient  and 
persevere.  Proficiency  in  this  method  is  acquired  only 
after  long  practice  and  constant  application. 

2.  Give  careful  attention  to  details. 

3.  Be  content  to  learn  step  by  step,  one  thing  at  a 
time,  and  be  sure  to  know  the  reason  why  for  every- 
thing. 


2O  PHOTOSCOPY. 

4.  You  will  be  much  benefited  by  following  the  ex- 
periments and  observations  mentioned  throughout  this 
work. 

5.  Do  not  fail  to  study  the  references. 

6.  Become    thoroughly    familiar   with    the    laws    of 
refraction  (Dioptrics)  and  reflection  (Catoptrics). 

7.  Remember,  that  without  a  good  understanding  of 
the  underlying  principles  the  test  must  remain  a  blind 
routine  and  can  never  be  of  the  highest  utility.     The 
fundamental  groundwork  must  be  understood  before 
the  test  can  be  appreciated. 

8.  It  is  wise  to  begin  the  study  of  the  test  under 
known  conditions.     Any  of  the  many  schematic  eyes  on 
the  market  can  be  used  for  this  purpose,  or  one  can 
easily  be  made. 

9.  After  studying  this  volume  thoroughly,  and  per- 
forming the  simple  experiments   advised  therein,  ex- 
amine a  series  of  ordinary  eyes  with  known  refractive 
defects,    such    as    simple    myopia,    hypermetropia,    or 
astigmatism.     Be  careful  to  follow  every  detail,   and 
make  a  close  study  of  the  areas  of  light  and  darkness 
in  the  pupil  under  as  many  different  conditions  as  possi- 
ble,— /.  e.y  with  different  sizes  of  the    light    aperture 
in  the  chimney;    with  the  source  of  light  at  different 
distances  from  the  mirror;   with  the  mirror  at  different 
distances  from  the  patient;    and  with  different  lenses 
before  the  eye  to  be  examined. 

10.  The  question  often  arises:    Should  the  ophthal- 
mologist wear  lenses  while  performing  this  test  ?     The 
writer  will  answer  this  question  by  stating  that  the  ex- 
aminer's distant  vision  should    be    at    least  f.     This 
should,   if  possible,   be   obtained   by   accommodating, 
rather  than  by  the  aid  of  correcting  lenses,  since  they  re- 


NECESSARY    INSTRUMENTS.  21 

fleet  more  or  less  of  the  rays  of  light;  but,  if  the  vision 
is  much  better  with  lenses  than  without,  they  should  be 
used.  The  examiner  does  not  need  to  take  any  note  of 
his  own  accommodation,  as  he  must  do  in  practising 
ophthalmoscopy  for  like  purposes. 

Necessary  Instruments. — i.  The  Photoscope,  or 
Mirror. — Many  varieties  of  the  photoscope  are  in  use. 
They  should  all  have  a  good-sized  round  handle,  four 
or  five  inches  long  and  from  one-fourth  to  one-half  inch 
in  diameter.  Some  prefer  a  mirror  with  a  small,  folding, 
protecting  handle,  or  two  mirrors,  so  made  that  one 
may  serve  for  the  handle  while  the  other  is  in  use. 
These  are  easily  carried  in  the  pocket,  but  the  writer 
much  prefers  one  with  a  long  handle,  because  it  is  easier 
to  hold  and  manipulate,  the  handle  lying  in  the  hollow 
of  the  hand  and  the  index  finger  resting  against  the 
edge  of  the  disc,  thus  giving  better  control  of  the  in- 
strument; while  in  holding  the  other  styles,  the  fingers 
are  cramped. 

The  silvering  on  the  mirror  should  be  free  from  im- 
perfections and  flaws,  so  that  the  reflections  may  be  as 
nearly  perfect  as  possible.  If  the  mirror  is  perforated 
in  the  center,  the  light  rays  pass  freely  to  the  examiner's 
eye,  but  the  edge  of  the  perforation,  unless  perfectly 
blackened  and  free  from  chipping,  causes  very  annoy- 
ing reflections.  These  objections  are  practically 
overcome  when  the  mercury  or  plating  alone  is  removed; 
but,  even  then,  the  glass  intercepts  and  reflects  some  of 
the  light  that  otherwise  would  pass  from  the  observed 
to  the  examiner's  eye.  The  central  dark  shadow, 
noticed  especially  when  the  light  is  reflected  on  a  white 
surface,  is  more  marked  the  larger  the  perforation,  but 
is  almost  eliminated  by  having,  instead  of  a  perforation, 


22 


PHOTOSCOPY. 


only  a  small  area  of  the  mercury  removed,  because  the 
unbroken  surface  of  the  glass  also  reflects  some  light. 
Where  the  mercury  only  is  removed,  that  portion  of 
the  glass  uncovered  must  be  kept  especially  clean. 

The  following  varieties  are  preferred  by  the  writer  in 
the  order  mentioned,  al- 
though many  others  are 
on  the  market: 

(a)  A  plane  mirror  2 
centimeters  in  diameter, 
with  a  2-millimeter  sight- 


FlG.  I.- — Thorington's  small 
plane  mirror. 


FIG.    2.  —  Large    plane    or  concave 
mirror. 


hole  made  by  removing  the  quicksilver  rather  than  by 
perforating  the  glass  (and  this  applies  to  all  mirrors), 
mounted  on  a  plain  black  metal  disc  4  centimeters  or 
more  in  diameter,  so  as  to  be  large  enough  to  shade 


NECESSARY    INSTRUMENTS. 


the  eye  from  the  light.     This  is  the  most  useful  form 
when  the  source  of  light  is  near  the  mirror  (Fig.  i). 

(&)  A  plane  mirror  about  4  centimeters  in  diameter 
with  a  2- or  3-millimeter  sight-hole.  This  is  the  most 
useful  form  when  the  source  of  light  is  behind  the  pa- 
tient's head  (Fig.  2). 

(c)  A  concave  mirror  about  4  centimeters  in  diameter 
with  a  2-  or  3-millimeter  sight- 
hole  (Fig  2).  It  is  well  to 
have  this  and  one  of  the  plane 
mirrors  mentioned  above,  al- 
though a  plane  mirror  is  all 
that  is  necessary. 

2.  The  Light. — This  should 
be  as  white,  clear,  and  steady 
as  possible. 

(a)  The    Welsbach    mantel 
is  best,  although  easily  broken. 

(&)  The  argand  burner  is 
used  by  many  surgeons. 

(c]  The  electric  light  with 
a  spiral  carbon,  inclosed  in 
frosted  glass  and  covered  by 
a  hood  with  a  round  opening 
(Fig.  3),  is  excellent. 

3.  An  Adjustable  Bracket. — (a)  An  extension  bracket 
that  may  be  swung  within  a  radius  of  several  feet,  hav- 
ing a  vertical  adjustment  of  at  least  8  inches.     This  is 
necessary  when  the   bracket   is   attached   to  the   wall 
behind  the  patient.     It  is  easily  moved  and  probably 
the  most  useful  form — manufactured  by  F.  A.  Hardy  & 
Co.,  Chicago  (Fig.  13). 

(b)  One  of  the  smaller,  commoner,  and  somewhat 


FIG.   3. — Electric   light   with 
twisted  carbon. 


PHOTOSCOPY. 


cheaper  brackets  will  answer  if  it  is  attached  to  the  wall 
at  the  examiner's  side,  or  to  the  wall  behind  the  patient, 
if  it  is  preferred  to  work  with  the  light  at  that  distance. 
4.  A  cover  chimney,  or  light  screen,  to  shade  the  tight, 
regulate  its  amount,  and  also  to  diminish  the  heat. 
When  using  the  light  behind  the  patient's  head  this  is 
not  absolutely  necessary,  but  desirable,  with  either  the 
plane  or  concave  mirror  (Fig.  4). 


FIG.  4. — Thorington's  asbestos 
chimney. 


FIG.  5. — Thorington's  asbestos 
chimney  with  iris  diaphragm. 


(a)  One  made  of  |-inch  asbestos,  6  centimeters  (about 
2\  inches)  in  diameter  by  21  centimeters  (S\  inches)  in 
height,  to  fit  over  an  ordinary  gas-lamp  chimney.  It 
has  a  3O-millimeter  opening  placed  opposite  the  bright- 
est part  of  the  light  and  covered  by  an  iris  diaphragm, 
which  is  controlled  by  an  ivory-tipped  lever  moving  on 
an  index,  regulating  the  size  of  the  opening  from  2  to  30 
millimeters  (Fig.  5).  (Thorington,  Jour.  Amer.  Med. 
Assoc.,  1898,  p.  1378.) 


NECESSARY    INSTRUMENTS. 


(b]  A  simple  asbestos  screen,  but  with  an  uncovered 
5-millimeter  opening.  This  is  generally  all  that  is 
necessary  in  working  with  the  light  close  to  the  mirror. 
A  mica  chimney  is  cheaper,  and  stands  the  heat  better 
than  one  of  glass,  hence  is  better  to  use  next  the  flame 
with  either  of  the  cover  chimneys  (Fig.  6). 

5.  The  Examiner's  Protecting  Shade. — When  work- 
ing with  the  light  close  to  the  mirror,  a  shade  is  needed 
to  protect  the  examiner's  eyes 
from  the  bright  light  which  other- 
wise must  flash  into  the  unused 
eye  while  using  the  mirror  before 
the  other  eye,  no  matter  how 
small  the  opening  in  the  cover 
chimney.  By  holding  a  book 
about  five  or  six  inches  away  from 
a  5-millimeter  opening  the  size 
of  the  area  of  light  projected  on 
it  may  be  noticed. 

I  have  made  a  small  shade 
(Ophthalmic  Record,  Feb.,  1904), 
black  on  one  side,  with  a  mirror 
on  the  other  side,  which  is  so 
placed  as  to  reflect  light  on  the 
trial  case,  as  well  as  to  shade 
the  observer's  unused  eye.  If  preferred,  the  shade 
can  be  made  a  dull  black  on  both  sides.  The  shade 
is  supported  by  a  ball-and-socket  joint  device  which 
may  be  attached  to  any  cover  chimney,  and  is  easily 
placed  in  any  position.  It  is  indispensable  for  the  good 
of  the  test  and  the  comfort  of  the  examiner  when  work- 
ing with  the  light  close  to  the  mirror — manufactured 
by  F.  A.  Hardy  &  Co.  (Figs.  6  and  13). 


FIG 

chimney 
shade. 


6.  —  Plain    cover 
and      author's 


26 


PHOTOSCOPY. 


6.  A  Good  Ordinary  Trial  Case. — It  is  a  great  ad- 
vantage to  have  one  with  a  large  number  of  different 
spheres.  The  lenses  should  be  clean,  and  as  free  from 
scratches  as  possible.  I  had  a  trial  case  made  by  the 
Julius  King  Opt.  Co.,  containing  44  pairs  each  of  con- 
vex and  concave  spheres  and  31  pairs  each  of  convex 
and  concave  cylinders  (Ophthalmic  Record,  Jan.,  1906). 
The  handles,  which  have  the  strength 
marked  on  each  side,  are  provided  with 
a  screw  so  that  the  lenses  may  be  turned 
or  new  ones  introduced.  The  cylin- 
ders have  no  ground  opaque  sides, 
the  axis  being  indicated  by  two  small 
whitened  holes  near  the  margin,  which 
one  may  very  readily  see  in  any  light. 
'The  prisms  are  likewise  marked,  except 
that  there  is  dnly  one  whitened  hole 
indicating  the  apex. 

7.  A  good  simple  trial  frame,  one 
that  may  be  properly  adjusted  before 
the  eyes,  so  that  the  patient  will  see 
through  the  center  of  the  inserted 
lenses,  and  yet  not  allow  them  so 
close  as  to  touch  the  lashes  or  become 
covered  with  moisture.  The  writer 
has  a  set  of  simple  drop  trial  frames, 
each  with  a  quite  different  nose  piece, 
with  the  degrees  plainly  marked  in 
white  on  blackened  steel.  These  are 
the  simplest,  lightest,  and  most  satisfactory  trial  frames 
made. 

8.  Meter   Stick. — Every    one    should    have    a    meter 
stick,  graduated  on  the  edge  in  dioptric  focal  lengths. 


FIG.  7. 
Wiirdcmann's  disc 


NECESSARY   INSTRUMENTS.  2"J 

I  have  a  three-sided  meter  stick  graduated  in  the  met- 
ric system,  in  inches,  in  dioptric  focal  lengths,  and  also 
giving  a  tangent  scale  with  which  to  measure  the  de- 
grees of  squint,  etc.  One  side  gives  the  dioptric  focal 
length  of  the  minus  sphere  to  be  added  to  the  result 
found  at  the  working  distance  in  this  test.  A  measuring 
tape  may  also  be  employed,  attached  to  the  trial  frame 
or  lens  disc  (Burnett). 

9.  A  Dark  Room. — It  must  be  one   from  which  all 
light  can  be  excluded,  so  that  none  reaches  the  eye  to  be 
examined,  or  the  mirror,  either  directly  or  by  reflection 
from  other  objects,  except  that  which  arises  from  the 
light  in  use,  thus  making  darker  the  portion  of  the  ret- 
ina surrounding  the  bright   illumination.     This   room 
should  be  as  large  as  possible.     Small  closets  and  sweat 
boxes  are  not  conducive  to   good  work,  and  exhaust 
both  examiner  and  patient.     The  general  examination 
room  darkened  by  close-fitting  shades  is  usually  the 
best  obtainable. 

10.  Dr.    H.   V.   Wiirdemann    (American  ^Journal  of 
Ophthalmology,   1891,   p.   223)   described   a  very  con- 
venient although  not  absolutely  necessary  instrument, 
called   Wiirdemann  s  disc.     One  side  contains  convex 
and  the  other  concave  lenses.     It  is  reversible,  and  can 
be  raised  or  lowered  by  the  patient  or  an  assistant, 
allowing  different  lenses  to  be  placed  before  the  eye. 
Its  smooth   broad  edge  rests   against  the  side  of  the 
patient's  nose  (Fig.  7). 


CHAPTER  II. 

UNDERLYING  PRINCIPLES.— PRINCIPLES  OF  PHOTO- 
SCOPY.—  BRILLIANCY  OF  THE  LIGHT  IN  THE 
PUPIL.— DEGREE  AND  RATE  OF  MOVEMENT.— 
MATHEMATICAL  POINT  OF  REVERSAL.  — EX- 
PERIMENTS AND  OBSERVATIONS. 

Underlying  Principles. — i.  It  is  the  light  reflected 
from  a  non-luminous  object  which  makes  it  visible. 
Therefore,  the  manner  in  which  the  reflected  light 
reaches  the  eye  is  of  more  importance  by  far  than  the 
manner  in  which  the  light  reaches  the  object. 

2.  Any  visible  object  may  be  said  to  be  composed  of 
one  or  more  points,  and  from  each  of  these  points,  rays 
(waves)  of  light  are  reflected  in  every  direction.  If  the 
object  consists  of  only  one  point,  then  there  is  but  a 
single  cone  composed  of  countless  rays  of  light.  The 
base  of  this  cone  fills  and  rests  in  the  pupil  of  the  eye; 
the  apex  is  at  the  object.  (The  light  rays  are  gradually 
refracted  by  the  different  media  through  which  they 
pass,  the  secondary  rays  crossing  the  axial  ray  between 
the  nodal  points  at  the  optic  center  and  not  exactly  in 
the  plane  of  the  pupil,  although  it  is  better,  for  the  sake 
of  simplicity,  to  consider  them  as  being  bent  in  this 
plane.)  If  an  object  is  composed  of  many  points,  then 
there  are  as  many  cones  as  points  in  the  object.  When 
a  point  in  a  visible  object  is  situated  at  a  distance  of 
twenty  feet  or  more,  the  rays  of  light  passing  into  the 
eye  from  that  particular  point  are  so  nearly  parallel 
(so-called  parallel  rays)  that  instead  of  forming  a  cone 

28 


UNDERLYING    PRINCIPLES.  29 

they  may  be  considered  as  forming  a  cylinder  or  solid 
rod  of  light. 

3.  Parallel  rays  of  light  are  focused  on  the  retina  of  an 
emmetropic  eye,  forming  a  cone  within  the  eye  (like  the 
sharpened  end  of  a  lead  pencil)  The  base  fills  the 
pupil;  its  apex  rests  on  the  retina.  In  this  condition 
the  rays  of  light  from  a  point  in  space  are  focused  as  a 


FIG.  8. — i,  The  fine  black  lines  represent  parallel  rays  of  light  entering 
an  emmetropic  eye  and  focusing  on  the  retina.  The  dotted  lines  represent 
the  same  rays  reflected  by  the  retina  and  passing  parallel  to  their  source. 
2,  Parallel  rays  of  light,  after  entering  a  myopic  eye,  focus  before  reaching 
the  retina,  and  crossing  one  another  at  the  focal  point,  form  a  round  area 
of  light  on  the  retina.  The  dotted  lines  show  how  the  reflected  rays  pass 
out  of  the  eye  from  any  one  of  the  points  of  the  retinal  illumination  (cen- 
tral portion  of  the  illumination  in  this  case)  and  come  to  a  focus  outside  the 
eye,  where  they  cross  and  form  another  cone  of  light.  3,  The  black  lines 
represent  parallel  rays  entering  a  hypermetropic  eye  and  they  are  seen  to 
impinge  on  the  retina  in  circular  form.  The  dotted  lines  represent  the  rays 
reflected  from  the  retina  which  pass  divergingly  into  space.  A  and  B  show 
the  two  forms  of  retinal  illumination  in  an  emmetropic,  simple  hyperme- 
tropic, and  myopic  eye.  C,  D,  E,  F,  G,  different  forms  of  retinal  illumi- 
nation found  in  cases  of  astigmatism. 

single  point  on  the  retina.  Rays  of  light  reflected  from 
this  particular  point  will  again  pass  off  or  out  of  the  eye 
parallel,  filling  the  pupil  and  forming  a  cylinder  in  space 
(Fig.  81). 

4.  Parallel  rays  of  light  passing  into  a  myopic  (long) 
eye,  are  focused  before  reaching  the  retina,  and  cross  at 
this  focal  point,  forming  a  secondary  cone.  Therefore, 
in  this  condition  there  are  two  cones  within  the  eye, 
their  apices  a  common  point.  The  base  of  one  cone 


30  PHOTOSCOPY. 

fills  the  pupil;  the  base  of  the  other  rests  in  a  circular 
form  on  the  retina.  In  this  condition,  a  point  in  space 
is  represented  by  a  diffusion  circle  on  the  retina,  and 
the  light  reflected  from  a  point  in  this  circular  area 
will  pass  out,  filling  the  pupil,  and  come  to  a  focus 
(anterior  focal  point)  somewhere  in  space.  It  forms 
a  cone  whose  base  rests  in  the  pupil,  and  whose  apex 
corresponds  to  the  anterior  focal  point  of  the  eye.  The 
light  rays,  after  crossing  at  this  anterior  focal  point  of 
the  eye  (apex  of  this  first  cone),  form  a  second  cone 
whose  apex  joins  the  apex  of  the  first  cone,  and  whose 
base,  therefore,  rests  in  infinity  (Fig.  82). 

5.  Parallel  rays  passing  into  a  hypermetropic  (short) 
eye  reach  the  retina  before  focusing  and  form  a  trun- 
cated cone  or  frustum,  the  large  end  of  which  fills  the 
pupil;    the  small  end  rests  as  a  diffusion  circle  on  the 
retina.     In  this  condition,  a  point  in  space  is  also  rep- 
resented by  a  diffusion   circle  on  the   retina,  and   the 
light  rays  reflected  from  a  point  in  this  circular  area 
pass  into  space  divergingly,  forming  a  truncated  cone, 
its  base  at  infinity,   its   smaller  end   filling   the   pupil 
(Fig.  8>). 

6.  In  regular  astigmatism,  the  light  passing  into  an 
eye  never  strikes  the  retina  as  a  point  (a  focus)  and  only 
as  a  circle  in  certain  cases  of  mixed  astigmatism.     It 
is  practically  always  between  these  two,  either  a  line 
or  any  gradation  from  a  line  to  nearly  a  circle  (Fig.  8, 
C,  D,  E,  F,  G).     If  parallel  light  rays  passing  through 
any  meridian  are  exactly  focused  on  the   retina,  the 
returning  rays  through  that  meridian  will  pass  off  as 
parallel  rays  to  their  original  source.     In  hypermetropic 
or  myopic  meridians  this  is  not  true.     In  hypermetrop- 
ic meridians  they  will  pass  off  divergingly;  in  myopic, 


UNDERLYING    PRINCIPLES.  3! 

convergingly;    in    both    cases    reaching    their    source 
modified  by  these  conditions  of  refraction  (Fig.  8). 

7.  In  myopia,  the  light  passing  from  an  illuminated 
point  on  the  retina  (a  point  of  the  so-called  retinal  illu- 
mination) forms  a  cone  outside  the  eye,  its  base  filling 
the  pupil,  its  apex  at  the  anterior  focal  point  of  the  eye 
(Fig.  82).     This  point  is  at  once  the  far  and  (unless  the 
eye  accommodates)  near  point  of  the  eye.     It  is  the  only 
point  at  which  the  eye  can  see  clearly  without  changing 
its  refractive  strength, — the  point  for  which  the  eye  is 
focused.     This  point  is  the  conjugate  focus  of  the  ret- 
ina, or  the  point  where  light  starting  from  the  retina 
would  focus   (the  so-called  point  of  reversal).     Light 
rays  passing  from  a  point  on  the  retina  through  any 
myopic  meridian  will  focus  in  front  of  the  eye  at  the 
anterior  focal  point  of  that  meridian.     These  rays  form 
a  triangular  sheet  of  light  outside  the  eye,  its  base  at 
the  pupil  in  that  meridian,  its  apex  at  the  anterior  focal 
point  of  the  same  meridian. 

8.  The   position   of  the   apex  of   the  cone   can    be 
changed;  or,  which  is  the  same  thing,  the  anterior  focal 
point  of  the  eye  in  myopia,  or  the  anterior  focal  point 
of   any    myopic    meridian.       It    is    moved    closer    to 
the  eye  by  convex  (  +  )  spherical  lenses,  or  caused  to 
recede  by  concave  ( — )  spherical  lenses  placed  in  front 
of  the  eye. 

The  light  rays  passing  out  from  any  eye,  whether 
passing  parallel  as  in  emmetropia,  or  divergingly  as  in 
hypermetropia,  can  be  made  to  focus  at  different  dis- 
tances in  front  of  the  eye  by  means  of  convex  (+) 
spherical  lenses  placed  in  front  of  it.  This  produces 
an  artificial  myopia. 

9.  By    means   of  photoscopy  the   examiner  can  tell 


32  PHOTOSCOPY. 

whether  or  not  the  light  passing  through  any  particular 
meridian  of  an  eye  has  focused  before  reaching  his  eye. 
In  case  it  has  focused  before  reaching  his  eye,  it  can  be 
made  to  focus  at  his  eye  by  means  of  concave  ( — ) 
spherical  lenses,  or  by  the  examiner  moving  forward  to 
the  focal  point.  In  case  the  light  rays  have  not  focused 
before  reaching  his  eye,  they  can  be  made  to  do  so  by 
the  use  of  convex  (+)  spherical  lenses.  In  other 
words,  the  examiner  can,  at  all  times,  tell  whether  the 
rays  coming  out  of  an  eye  have  or  have  not  crossed 
before  reaching  his  eye.  They  can  be  made  to  cross 
at  his  eye  by  means  of  the  proper  spherical  lenses,  or 
sometimes  by  changing  his  position,  or  both. 

10.  When  light  strikes  a  mirror  or  a  reflecting  sur- 
face perpendicularly,  it  is  reflected  in  the  same  general 
direction  whence  it  came.     Light  passing  into  an  eye 
from  directly  in  front  strikes  the  retina  perpendicularly, 
and   is   reflected   in  the   same  general   direction,  only 
necessarily  somewhat  diffused.     Of  course,  the  retina, 
chorioid,  sclerotic,  and  nerve  ending  are  not  perfect 
reflecting  substances, — all   these   absorb   some  of  the 
light, — and,  their   surfaces   not    being   smooth,  reflect 
part  of  the  light  into  every  portion  of  the  interior  of  the 
eye.     So,  when  a  mirror  throws  light  into  an  eye,  some 
of  the  light  will  be  reflected  back  to  the  mirror.     If  the 
rays  reflected  through  the  patient's  pupil  focus  at  the 
mirror,  they  can  be  seen  by  the  examiner's  eye  only 
when  directly  behind  its  sight  hole  (Fig.  16).      But  if 
they  are  diffused,  as  in  high  degrees  of  ametropia,  they 
can  be  seen  sometimes  at  the  side  of  the  mirror. 

1 1 .  Light  from  a  source  above  a  window  will  pass 
into  a  room  in  a  downward  direction,  illuminating  the 
floor  or  lower  part  of  the  wall  opposite.     Conversely, 


UNDERLYING    PRINCIPLES.  33 

light  starting  from  the  lower  part  of  the  room  will  pass 
out  of  this  window  into  space  in  an  upward  direction. 
Hence,  a  person  standing  outside  of  the  room  could  see 
the  light  on  the  floor  only  by  being  above  the  level  of  the 
window. 

12.  Light  passing  into  a   room  from  a  source  lower 
than  the  window  will  illuminate  the  upper  part  of  the 
wall,  or  ceiling;.     The  light,  when   again   reflected  out 

O  O         7  O 

of  the  room,  can  be  seen  only  from  below. 

13.  When  a  lighted  lamp  is  seen  through  a  window, 
the  light  does  not  appear  to  occupy  the  whole  window, 
but  only  a  part  of  it.     It  appears  to  occupy  only  that 
part  through  which  the  light  is  seen.     This  part  may 
change  to  as  many  different  sections  of  the  window  as 
there    are    positions    from   which   the   light   is   visible. 
Light  rays  pass  from  the  lamp  out  of  every  part  of  the 
window.     If  a  large  convex  spherical  lens  were  placed 
before  the  window,  bringing  all  these  rays  of  light  to  a 
focus,  then,  viewed  from  that  point,  the  whole  window 
would  appear  occupied  by  one  large  light,  because  light 
from  every  part  of  the  window  would  enter  the  eye. 
However,  if  the  observer  were  not  at  the  point  of  focus- 
ing, only  a  part  of  the  window  would  appear  to  be  oc- 
cupied by  a  light.     This  part  would  change  its  location 
as  he  changed  his  position  in  front  of  the  window,  or 
as  the  light  was  moved.     If  the  observer  looked  directly 
through  the  center  of  the  lens  at  a  light,  a  magnified 
image  of  it  would  be  seen  in  the  same  direction.      But 

O 

if  he  looked  through  any  peripheral  portion  of  the  lens 
a  magnified  image  of  the  light  would  be  projected  in  a 
different  direction  from  the  true  position  of  the  light, 
because  all  spherical  lenses  have  a  prismatic  effect 
when  rays  of  light  pass  through  their  periphery.  If  he 


34  PHOTOSCOPY. 

looked  through  the  upper  portion  of  the  lens,  the  image 
would  be  displaced  upward ;  if  through  the  lower,  down- 
ward. 

14.  If  the  eye  is  likened  to  a  room,  the  pupil  being  a 
round  window,  the  retina  forms  the  back  and  sides  of 
the  room.     The  light  in  entering  an  eye  always  passes 
through  every  portion  of  the  whole  pupil;  and,  in  being 
reflected   out,   likewise   passes   through   every   portion. 
Light  coming  from  a  source  above  the  center  of  the 
pupil  strikes  the  retina  below  its  center,  and  the  light 
from   below  impinges  on  the   retina   above.     Neither 
the  lens   nor  the  other  refractive   media   change  this 
general  statement. 

15.  Consider  this   light  on  the  retina   (retinal   illu- 
mination) as  a  lamp  placed   in  the  eye,  for  it  is  the 
source  of  light  that  passes  to  the  examiner's  eye  in  this 
test.     If  this  retinal  illumination  is  above  the  central 
part  of  the  retina,  the  general  direction  of  the  light  pass- 
ing out  of  the  eye  will  be  downward.     But  if  it  is  below, 
the  light  will  pass  upward;    if  on  the  right,  light  will 
pass  to  the  left;  and  if  on  the  left,  then  toward  the  right. 

16.  The  part  of  the  window,  or  pupil,  that  appears 
brightly  illuminated  is  the  part  through  which  bright 
light  rays  pass  to  the  observer's  eye.     The  dark  portion 
is  the  part  through  which  the  light  reflected  from  the 
retinal  illumination  does  not  pass  into  his  eye  but  into 
space.     The  only  rays  which  do  pass  through  this  dark 
portion  of  the  pupil  and  enter  the  examiner's  eye  are 
those  which  come  from  the  dimly  illuminated  portion 
of   the    retina    immediately    surrounding    the    bright 
retinal  illumination. 

Principles  of  Photoscopy. — Recalling  the  illustra- 
tion in  which  the  eye  was  likened  to  a  room,  and  the 


PRINCIPLES  OF  PHOTOSCOPY. 


35 


pupil  to  a  window  of  this  room,  the  use  of  the  different 
forms  of  mirrors  in  reflecting  light  through  the  pupil 
into  the  eye  can  now  be  considered. 

When  a  plane  mirror  is  held  perpendicularly  in  front 
of  an  eye  and  on  a  level  with  it,  only  rays  of  light  which 
are  reflected  from  the  central  portion  of  the  mirror 
enter  the  observed  eye.  Now,  if  the  mirror  be  tilted 
downward,  the  light  on  the  face  moves  down,  and  only 


FIG.  9.— Plane  mirror  tilted  downward.  AB,  plane  mirror  tilted  down- 
ward, reflecting  the  light  coming  from  the  aperture  in  the  cover  chimney 
down  on  the  face,  as  indicated  by  the  large  arrow,  and  down  on  the  retina, 
as  indicated  by  the  small  one.  The  light  which  enters  the  pupil,  when 
traced  back  by  the  dotted  lines,  comes  only  from  the  upper  part  of  the  mir- 
ror, as  in  M.  The  image  of  the  light,  or  apparent  source  of  light,  is  erect, 
since  the  rays  forming  it  have  not  crossed,  and  is  apparently  situated  behind 
the  mirror  in  the  direction  from  which  the  rays  enter  the  eye.  The  dis- 
tance between  the  mirror  and  R  (the  image)  should  be  the  same  as  between 
the  mirror  and  the  source  of  light,  but  if  made  so  the  diagram  would  be  less 
effective  in  some  other  particulars. 

the  upper  rays  of  light,  which  are  reflected  from  the  upper 
part  of  the  mirror,  enter  the  patient's  eye.  If  the 
patient  is  asked  in  what  portion  of  the  mirror  he  sees 
the  light,  he  will  answer  that  he  sees  it  in  the  upper,  for 
the  reason  that  the  tilting  has  caused  the  apparent 
source  of  light,  or  image  of  the  light  in  the  mirror,  to 
move  from  the  central  to  the  upper  portion  (Fig.  9). 
The  light  which  enters  the  patient's  eye  comes  from 
above  the  central  portion  of  the  pupil,  and  therefore 


30  PHOTOSCOPY. 

must  impinge  on  the  retina  below  its  center.  The 
mirror  has  been  tilted  downward;  the  light  on  both  face 
and  retina  has  moved  down. 

Exactly  the  reverse  is  obtained  when  the  mirror  is 
tilted  upward.  The  apparent  source  of  light  is  now  seen 
by  the  patient  in  the  lower  portion,  and  the  light  which 
enters  the  eye  comes  from  the  same  portion,  which  is 
below  the  center  of  the  pupil;  therefore,  it  must  im- 


FIG.  10. — Plane  mirror  tilted  upward.  The  large  arrow  indicates  the 
movement  of  the  light  on  the  face,  the  small  one  of  the  retinal  illumination, 
both  being  in  the  same  direction.  The  light  which  enters  the  patient's  eye, 
indicated  by  the  dotted  lines,  comes  directly,  without  crossing,  from  the 
lower  part  of  the  mirror,  and  hence  the  apparent  source  of  light  or  erect 
image  of  the  light  is  seen  by  the  patient  in  the  lower  part  of  the  mirror  M, 
and  apparently  behind  it  at  R.  Note  that  in  Fig.  9  the  light  entering  the 
pupil  is  reflected  by  the  upper  part  of  the  mirror,  and  in  this  by  the  lower, 
giving  the  same  result  as  if  a  light  had  been  lowered  in  front  of  the  eye, 
thus  raising  the  retinal  illumination.  The  distance  between  the  mirror  and 
R  should  be  the  same  as  between  the  mirror  and  the  source  of  light.  (Ex- 
planation in  Fig.  9.) 


pinge  on  the  retina  above  the  center.  The  mirror  has 
been  tilted  upward,  and  the  light  on  the  face  and  retina 
has  moved  in  the  same  direction  (Fig.  10). 

If  the  light  rays  extending  from  the  apparent  source 
of  light  to  the  retina  are  likened  to  a  lever,  the  pupil  to 
the  fulcrum,  and  the  mirror  to  the  power  arm  to  raise 
and  lower  the  external  end  or  apparent  source  of  light, 
it  will  be  seen  that  the  retinal  or  internal  end  must 
move  in  the  opposite  direction. 


PRINCIPLES  OF  PHOTOSCOPY.  37 

No  matter  what  the  refractive  condition  of  the  eye 
may  be  (myopic,  hypermetropic,  astigmatic,  or  emmetro- 
pic),  light  passing  from  a  plane  mirror,  when  it  is  tilted 
in  any  direction,  causes  the  light  on  the  face  and  that  on 
the  retina  (retinal  illumination)  to  move  in  the  same 
direction  (Figs.  9  and  10). 

The  image  of  any  object  seen  in  a  plane  mirror  is 
apparently  as  far  back  of  the  mirror  as  the  object  is  in 
front  of  it;  therefore,  the  image  of  the  light  seen  in  the 
mirror  by  the  patient  is  apparently  as  far  back  of  the 
mirror  as  the  source  of  light  is  in  front  of  it.  The  light 
enters  the  patient's  eye  from  the  same  direction  and 
distance,  in  exactly  the  same  manner  as  if  the  light  were 
placed  at  the  apparent  source  (image  of  light  in  the 
mirror).  In  other  words,  the  light  enters  the  patient's 
eye  from  a  distance  equal  to  the  distance  from  the  pa- 
tient's eye  to  the  mirror  plus  the  distance  from  the  mirror 
to  the  source  of  light.  The  amount  and  brilliancy  of 
light  entering  the  patient's  eye  is  in  inverse  ratio  to  the 
square  of  the  distance  of  the  apparent  source  of  light, 
or  image  of  the  light  in  the  mirror,  from  the  eye.  For 
example:  if  the  apparent  source  of  light  is  at  2  meters, 
there  is  four  times  as  much  light  as  when  it  is  at  4 
meters,  or  twice  the  distance.  If  the  mirror  is  I  meter 
distant  from  the  eye,  and  the  source  of  light  i  meter 
from  the  mirror,  then  the  image,  or  apparent  source  of 
light,  is  2  meters  from  the  eye.  Now,  if  the  light  is 
moved  3  meters  from  the  mirror,  the  position  of  the 
mirror  remaining  exactly  the  same,  or,  on  the  other 
hand,  the  mirror  moved  2  meters  from  both  patient's 
eye  and  lamp,  the  image  (or  this  apparent  source  of  light) 
will  be  4  meters  from  the  eye.  In  either  case  it  is  twice 
as  far  as  in  the  first  instance,  and,  as  the  square  of 


38  PHOTOSCOPY. 

two  is  four,  there  will  be  only  one-fourth  as  much  light 
passing  into  the  eye. 

It  has  already  been  stated  that  the  light  enters  the 
patient's  eye  as  if  it  came  from  the  image,  or  apparent 
source  of  light  in  the  mirror.  If  the  anterior  focal 
point,  or  conjugate  focus  of  the  retina,  and  the  apparent 
source  of  light  should  coincide — /.  e.,  be  located  in  the 
same  spot — the  light  would  focus  on  the  retina  and 
give  a  small  bright  area  of  retinal  illumination,  which 
would  reflect  the  light  better,  and  give  a  more  distinct 
anterior  focal  point  than  a  large  and  less  brilliant 
illumination.  Therefore,  when  working  near  the  an- 
terior focal  point,  it  is  desirable  that  the  apparent  source 
of  light  should  be  as  near  this  position  as  possible.  The 
brighter  the  source  of  light  and  the  nearer  the  apparent 
— not  the  real — source  is  to  the  eye  the  more  light  enters 
the  eye.  The  closer  the  apparent  source  of  light  is  to 
the  anterion^ocal  point  the  more  nearly  the  light  focuses 
on  the  retina,  or  the  smaller  is  the  retinal  illumination. 

When  a  concave  mirror  is  held  perpendicularly  in 
front  of,  and  on  a  level  with  the  eye,  but  at  a  distance 
greater  than  its  focal  length,  only  the  central  rays  of 
light  enter  the  eye.  These  rays  come  from  the  central 
portion  of  the  mirror.  Now,  if  the  mirror  is  tilted  down- 
ward, the  light  on  the  face  moves  down,  as  it  did  with 
the  plane  mirror.  But,  unlike  with  the  latter,  the  ap- 
parent source  of  light,  or  image  of  the  light,  which  is 
situated  in  front  of  the  mirror  also  moves  down.  The 
upper  rays  on  the  patient's  face  which  pass  into  the  eye, 
if  traced  back,  come  from  the  lower  part  of  the  mirror, 
and  having  crossed,  the  patient  on  being  asked  will  say 
that  the  image  of  the  light  is  in  the  lower  part  of  the 
mirror. 


PRINCIPLES  OF  PHOTOSCOPY. 


39 


The  light  reflected  from  the  lower  portion  of  the 
mirror  is  focused  with  that  coming  from  other  portions, 
and  passes  from  below  through  the  pupil  in  an  upward 
direction,  impinging  on  the  retina  above  its  center.  If 
the  concave  mirror  is  tilted  downward,  the  light  on  the 

*  O 

face  moves  down,  but  that  on  the  retina  up  (Fig.  n). 
If  the  mirror  is  tilted  upward,  the  apparent  source  of 


M 


FIG.  ii.  —  Concave  mirror  tilted  downward:  The  large  arrow  indicates 
the  movement  of  the  light  on  the  face,  in  the  same  direction  as  with  the 
plane  mirror,  but  is  opposite  to  the  direction  of  the  small  arrow,  indicating 
the  movement  of  the  light  on  the  retina,  or  the  retinal  illumination.  The 
reason  for  this  difference  between  the  plane  and  concave  mirrors  is  that  while 
the  upper  part  of  the  light  at  the  face  enters  the  pupil  in  each  case,  with 
the  plane  it  is  reflected  directly  from  the  upper  part  of  the  mirror,  but  with 
the  concave  from  the  lower  part,  having  crossed.  The  apparent  source  or 
image,  which  is  inverted  because  the  rays  forming  it  have  crossed,  appears 
to  be  in  the  lower  part  of  the  mirror,  and  in  front  of  it,  near  its  focal  point. 
M  shows  the  part  of  the  mirror  which  reflects  the  light. 


light  moves  up,  and  the  light  passes  into  the  eye  in  a 
downward  direction,  coming  from  the  upper  portion 
of  the  mirror  and  impinging  on  the  retina  below  the 
center.  If  the  concave  mirror  is  tilted  upward,  the 
light  on  the  face  moves  up,  and  the  light  on  the  retina 
moves  down  (Fig.  12). 

With  the  concave  mirror,  unless  its  focal  length  is 


40  PHOTOSCOPY. 

very  short,  the  focus  of  the  light,  or  apparent  source  of 
light,  is  close  to  the  patient's  eye,  and  therefore  a  large 
amount  of  light  will  pass  into  the  eye.  In  using  the 
plane  mirror,  the  light  on  both  face  and  retina  moves  in 
the  same  direction,  thus  corresponding  with  the  move- 
ments of  the  mirror.  But,  with  the  concave  mirror,  the 
light  on  the  face  moves  in  the  same  direction,  while  the 
light  on  the  retina  moves  in  the  opposite  direction  to  the 


FIG.  12.  —  Concave  mirror  tilted  upward:  The  large  arrow  pointing 
upward  and  the  small  one  downward  show  that  the  light  on  the  face  and  ret- 
ina moves  in  opposite  directions.  The  lower  part  of  the  light  on  the  face 
enters  the  pupil  as  with  the  plane  mirror  (Fig.  10),  but  comes  from  the  upper 
part  of  the  mirror,  having  crossed,  as  shown  by  the  dotted  lines.  The 
patient  sees  the  image,  apparent  source  of  light,  in  the  direction  of  the  upper 
part  of  the  mirror  and  near  its  point  of  focus.  The  image  is  inverted,  be- 
cause the  rays  forming  it  have  crossed.  M  shows  the  part  of  the  mirror 
which  reflects  the  light. 


movement  of  the  mirror.  To  repeat, — the  light  on  the 
retina  moves  in  the  same  direction  as  the  light  on  the 
face  with  the  plane  mirror;  but  in  the  opposite,  with 
the  concave,  in  any  eye  (Figs.  9,  10,  n,  and  12). 

Not  only  the  means  but  also  the  manner  in  which  the 
light  enters  the  patient's  eye  and  impinges  upon  the 
retina  have  been  carefully  considered.  The  more  im- 
portant part  of  this  test  can  now  be  taken  up, — /'.  e.,  the 


PRINCIPLES  OF  PHOTOSCOPY.  4! 

manner  in  which  the  light,  reflected  from  the  patient's 
retina,  passes  to  the  examiner's  eye.* 

Consider  the  light  illumination  on  the  retina  as  a 
small  lamp  placed  at  the  back  of  the  eye,  which  can  be 
moved  up  and  down  or  from  side  to  side,  by  tilting  the 
mirror.  It  is  now  important  to  learn  how  the  light 
passes  out  of  the  eye  from  this  retinal  lamp,  or  illumina- 
tion. It  will  be  well,  for  a  time  at  least,  not  to  think 
of  how  the  light  entered  the  eye  to  form  this  retinal 
illumination  (which  has  just  been  considered),  as  it  has 
practically  nothing  to  do  with  the  manner  of  its  exit. 

The  light  passes  out  of  the  eye  through  every  portion 
of  the  pupil,  no  matter  whether  this  is  from  the  single 
point  of  a  perfect  focus  of  light  on  the  retina  or  from 
each  of  the  several  points  of  a  so-called  imperfect  focus. 
These  rays  of  light  will  either  focus  in  front  of  the  eye 
or  pass  parallel  or  divergingly  into  space,  and  in  every 
case  will  form  an  area  of  light,  large  or  small,  at  the  ob- 
server's face.  Some  or  all  of  these  rays  will  pass  through 
the  aperture  of  the  mirror  into  the  observer's  eye. 

The  same  laws  govern  the  light  in  passing  out  as  were 
observed  in  our  consideration  of  light  passing  into  the 
eye, — i.  e.,  if  the  retinal  illumination  is  above  the  center  of 
the  retina,  the  light  rays  will  pass  out  in  a  downward 
direction;  if  below,  in  an  upward  direction;  if  to  the 
left,  then  to  the  right;  and,  if  to  the  right,  then  to  the 
left. 

The  observer  is  concerned  only  with  the  central  light 
image  or  spot  apparently  in  the  pupil  of  the  observed 
eye,  in  considering  its  apparent  size,  shape,  brilliancy, 
and  rate  of  movement.  This  portion  in  the  observed 
eye,  which  appears  light  to  the  examiner,  is  in  a  direct 

*  In  this  connection  the  sight-hole  in  the  mirror  need  not  be  considered. 
5 


42  PHOTOSCOPY. 

line  from  his  nodal  point  to  that  part  of  the  pupil  through 
which  the  light  from  the  real  retinal  illumination  passes 
to  enter  the  examiner's  eye;  it  is  simply  projected  in  the 
direction  from  which  the  rays  of  light  come.  The 
apparent  darkness  which  surrounds  the  central  light 
area  in  the  pupil  of  the  observed  eye  appears  dark 
only  because  the  bright  light  from  the  retinal  illumina- 
tion, although  passing  through  this  area  of  the  pupil, 
does  not  enter  the  observer's  eye.  The  few  rays  of 
light  which  do  pass  through  the  dark  portion  of  the 
pupil  into  the  examiner's  eye,  as  before  stated,  are  re- 
flected by  the  dark  or  dimly  illuminated  portion  of  the 
retina  which  surrounds  the  bright  retinal  illumination. 
The  dark  part  of  the  pupil  might  be  termed  a  poor 
image  of  a  portion  of  the  dimly  illuminated  retina. 

In  the  remainder  of  this  book,  the  rays  of  light  pass- 
ing from  the  bright  illumination  on  the  retina  will  alone 
be  considered.  And,  in  order  to  make  the  test  simpler 
and  easier  to  understand,  it  will  be  assumed  that  the 
portion  of  the  retina  surrounding  the  bright  retinal 
illumination  is  in  complete  darkness,  and  that  no  light 
rays  are  reflected  by  it  through  the  dark  portion  of  the 
pupil  into  the  examiner's  eye. 

If  the  whole  retina  were  equally  illuminated,  the  whole 
pupil  would  appear  equally  filled  with  light,  as  the 
observer  would  see  a  magnified  image  of  some  portion 
of  the  illuminated  retina  through  every  part  of  the  pupil. 
But,  since  in  the  test  only  a  small  part  of  the  retina  is 
brightly  illuminated,  only  that  part  of  the  pupil  appears 
brightly  lighted  through  which  the  image  of  this  por- 
tion of  the  retina  is  seen. 

The  diagrams  in  this  book,  for  the  sake  of  clearness, 
represent  the  retinal  illumination  as  a  mere  point  of 


PRINCIPLES  OF  PHOTOSCOPY.  43 

light,  but  this  illuminated  area  is  usually  either  round  or 
elliptical  in  shape  with  a  more  or  less  blurred  margin 
between  the  brighter  central  and  surrounding  dark 
portion  of  the  retina.  The  light,  passing  through  the 
pupil  to  the  examiner's  eye,  comes  from  this  more  or 
less  blurred-edged  disc  of  light  on  the  retina,  and  the 
observer  finds  it  more  difficult  to  distinguish  the  divid- 
ing line  between  the  central  area  and  surrounding 
shaded  area  when  the  margins  of  the  central  bright 
area  are  not  defined.  Hence,  it  is  important  to  have 
a  small  and  bright  retinal  illumination,  and  the  remain- 
der of  the  retina  as  little  illuminated  as  possible,  with 
as  distinct  a  margin  between  the  illuminated  and  dark 
portions  as  can  be  secured. 

When  all  the  rays  of  light  passing  out  of  the  patient's 
eye  focus  in  the  examiner's  eye,  or  are  focused  there  by 
spherical  lenses,  he  being  at  the  anterior  focal  point, 
the  pupil  of  the  observed  eye  will  necessarily  appear 
brilliantly  illuminated  as  a  bright,  large,  central  light 
area.  Since  there  is  no  dark  portion  with  which  to  com- 
pare this  light  area,  no  movement  of  this  area  is  appar- 
ent (Fig.  1 6). 

If  the  rays  of  light  are  not  brought  to  a  focus  at  the 
examiner's  eye,  only  a  part  of  them  enter  his  eye. 

The  following  phenomena  will  be  observed  when  the 
rays  of  light  have  not  focused  before  reaching  the  ex- 
aminer's eye, — /'.  e.,  when  the  anterior  focal  point  (if 
there  be  one)  is  behind  the  examiner,  always  indicating 
that  a  convex  (-)-)  spherical  lens  is  required  for  the  cor- 
rection, as  in  hypermetropia  and  emmetropia,  or  myo- 
pia when  the  anterior  focal  point  is  situated  at  a  dis- 
tance greater  than  that  of  the  examiner  (Figs.  14,  15, 
17,  and  18). 


44  PHOTOSCOPY. 

1.  Only  a  certain  number  of  the  rays  of  light,  re- 
flected from  the  retinal  illumination  and  passing  out  of 
the  pupil,  enter  the  examiner's  eye. 

2.  The  rays  passing  from  the  retinal  illumination, 
which  do  enter  the  examiner's  eye,  pass  through  that 
portion  of  the  pupil  which  alone  appears  brightly  illu- 
minated   (light    area   or   image).     This    light    area   is 
simply  projected  in  the  direction  of  the  rays  of  light, 
like  any  image  seen  through  a  lens  or  prism. 

3.  The  bright  rays  which  do  not  enter  his  eye  pass 
through  that  portion  of  the  patient's  pupil  which  ap- 
pears dark — the  so-called  shadow. 

4.  The  portion  of  the  pupil  which  appears  illuminated 
corresponds  in  position  to  the  situation  of  the  examiner's 
eye  in  the  area  of  light  at  the  examiner's  face,  and  also 
to  the  location  of  the  illumination  on  the  retina  from 
which  these  rays  come.     Thus,  if  the  retinal  illumina- 
tion is  above  the  center  of  the  retina,  the  rays  pass  out 
in  a  downward  direction.     Only  the  upper  portion  of 
these  rays  enters  the  examiner's  eye  and  passes  through 
the  upper  portion  of  the  patient's  pupil,  which  part 
alone  appears  brightly  illuminated  (Figs.  15  and  18). 

If  the  rays  of  light  have  focused  before  reaching  the 
examiner's  eye,  forming  an  anterior  focal  point  in  front 
of  his  eye,  between  him  and  the  patient,  as  in  high  de- 
grees of  myopia,  it  indicates  that  a  concave  ( — )  lens  is 
required  for  correction.  At  the  anterior  focal  point  the 
rays  cross, — the  lower  rays  now  become  the  upper,  and 
the  upper  the  lower;  the  right  the  left,  and  the  left 
the  right  ones  (Figs.  19  and  20). 

In  this  condition  the  following  will  be  observed : 
i.  Only  a  certain  number  of  the  total  rays  of  light 
reflected  out  of  the  patient's  pupil  enter  the  examiner's 
eye. 


BRILLIANCY   OF   THE    LIGHT    IN   THE    PUPIL.         45 

2.  The  bright  rays  of  light  which  enter  the  examiner's 
eye  pass  through  that  portion  of  the  pupil  which  alone 
appears  brightly  illuminated. 

3.  The  bright  rays  of  light  which  do  not  enter  the 
observer's  eye  pass  through  that  portion  of  the  pupil 
which  appears  dark. 

4.  The  illuminated   portion  of  the   pupil   does   not 
correspond  in  position  to  the  situation  of  the  examiner's 
eye  in  the  area  of  light  at  his  face,  neither  to  the  lo- 
cation of  the  illumination  on  the  retina  from  which 
these  rays  come.     That  is  to  say,  if  the  retinal  illumina- 
tion is  above  the  center  of  the  retina,  the  rays  will  pass 
out  in  a  downward  direction,  cross  at  the  anterior  focal 
point,  and  their  position  is  now  reversed  as  stated  above. 
Therefore,  only  the  upper  portion  of  the  rays,   after 
crossing,  enter  the  examiner's  eye.     These  latter  rays 
have  passed  through  the  lower  illuminated  portion  of 
the  pupil  (Fig.  20). 

The  Brilliancy  of  the  Light  in  the  Pupil. — The 
brilliancy  of  the  central  light  area  or  image  is  dependent 
on  several  factors : 

1.  The  brightness  of  the  true  illumination  on  the 
retina  (pages  3 7,  38). 

2.  The  distance  of  the  mirror  from  the  source  of 
light  and  of  the  mirror  from  the  patient,  the  light  be- 
coming brighter  as  this  distance  is  lessened. 

3.  The  proximity  to  the  anterior  focal  point.     When 
at  this  point,  all  the  rays  of  light  passing  out  of  the  pa- 
tient's pupil  are  nearly  focused  into  the  examiner's  eye, 
but  this  increase  in  brilliancy  is  somewhat  counterbal- 
anced by  the  fact  that  the  light  comes  from  a  smaller 
portion  of  the  true  retinal  illumination. 

4.  The  degree  to  which  the  brightness  of  the  impor- 


46  PHOTOSCOPY. 

tant  central  portion  of  the  retinal  illumination  is  di- 
minished by  the  sight  hole  in  the  mirror. 

When  the  surgeon  is  at  the  anterior  focal  point  he 
receives  light  from  a  very  small  portion  of  the  retinal 
illumination,  but  the  farther  he  is  from  this  point  the 
larger  the  area  of  the  retina  which  reflects  light  to  his  eye. 

Degree  and  Rate  of  Movement.  —  Recalling  the 
fact  that  the  light  rays  were  likened  to  a  lever  and  the 
pupil  to  its  fulcrum,  if  the  external  end  of  this  lever  is 
moved  six  inches,  the  internal  end  moves  twice  as  far 
as  when  the  external  end  is  moved  three  inches.  Now, 
if  the  same  rate  of  movement  is  used  in  both  cases,  it 
will  be  seen  that  it  must  take  twice  as  long  in  the  first 
as  it  does  in  the  second  case;  and,  if  the  light  area  at  the 
examiner's  face  in  one  condition  is  twice  the  size  of 
that  in  another,  it  is  easily  understood  that  the  retinal 
illumination  must  move  twice  as  far  in  one  case  as  in  the 
other,  and  if  moved  at  the  same  rate,  it  must  take  twice 
as  much  time;  therefore,  the  central  light  area  will  take 
twice  the  time  to  move  aross  the  pupil.  The  nearer  the 
examiner's  eye  is  to  the  anterior  focal  point  of  an  eye, 
the  smaller  the  area  of  light  at  the  examiner's  face, 
therefore,  the  easier  it  is  to  move  this  area  across  the  eye, 
requiring  less  change  of  position  of  the  illumination  on 
the  retina,  and  consequently  less  tilting  of  the  mirror 
and  correspondingly  less  time.  The  whole  depends  on 
the  size  of  the  light  area  at  the  examiner's  face. 

The  rate  of  movement  of  the  central  light  area  in  the 
pupil  also  depends  on  the  rate  of  movement  of  the 
retinal  illumination,  the  latter  being  influenced  by— 

1.  The  rate  of  movement  of  the  mirror. 

2.  Differences  in  the  distance  of  the  light  from  the 
mirror,  and  the  mirror  from  the  eye. 


MATHEMATICAL    POINT    OF    REVERSAL.  47 

3.  The  distance  of  the  nodal  points  from  the  retina. 
This  will  be  readily  understood  by  likening  the  rays  of 
light  entering  the  eye  to  a  lever  and  the  nodal  points  to 
its  fulcrum.  It  will  then  be  seen  that  the  shorter  the 
external  end  extending  from  the  nodal  points  to  the 
apparent  source  of  light,  and  the  longer  the  internal 
portion  of  the  lever  between  the  nodal  points  and  the 
retina,  the  more  rapid  will  be  the  movement  of  the  inner 
arm.  The  posterior  end  of  the  latter  corresponds  to 
the  retinal  illumination. 

The  Mathematical  Point  of  Reversal.  —  This  is 
never  found  in  actual  practice,  but  only  in  theory  in  an 
ideal  or  standard  eye.  The  light  reflected  from  the 
fundus  of  the  patient's  eye  passes  out  and  forms  an  area 
of  light  at  the  examiner's  face.  If  this  area  is  much 
larger  than  the  examiner's  pupil,  only  a  certain  amount 
of  the  light  enters  his  pupil,  and  the  portion  of  the  pa- 
tient's pupil  through  which  these  rays  pass  alone  ap- 
pears brightly  illuminated.  The  remainder  of  the 
patient's  pupil  appears  slightly  darker.  If  all  the  rays 
of  light  reflected  from  the  patient's  fundus  would  focus 
at  or  pass  into  the  observer's  pupil,  he  would  receive 
rays  of  light  through  every  part  of  the  patient's  pupil 
which  therefore  would  appear  completely  illuminated, 
and  he  would  be  at  the  practical  point  of  reversal.  If 
the  examiner  could  dilate  his  pupil  ad  libitum  so  as  to 
make  it  correspond  to  the  area  of  light  on  his  face,  the 
patient's  pupil  would  always  appear  fully  illuminated. 
It  is  thus  seen  that  whenever  the  observer's  pupil  re- 
ceives all  the  rays  of  light,  the  observer  is  at  the  practical 
point  of  reversal.  However,  in  this  ideal  mathematical 
condition  under  consideration,  a  perfect  anterior  focal 
point,  or  point  of  reversal  coinciding  with  a  pin-point 


48  PHOTOSCOPY. 

pupil,  must  be  imagined.  The  secondary  rays  of  light 
will  necessarily  cross  one  another  at  this  perfect  focus 
through  this  pin-point  sized  pupil,  thus  making  the 
nodal  point  coincide  with  the  location  of  the  pupil  and 
point  of  reversal.  Mathematically,  they  all  coincide;  al- 
though in  practice  the  pupil  is  the  determining  factor, 
the  nodal  points  being  located  behind  the  plane  of  the 
pupil. 

Experiments  and  Observations. — The  author  rec- 
ommends the  carrying  out  of  the  following  experi- 
ments and  observations,  since  they  will  aid  in  the 
proper  understanding  of  the  test: 

1.  Blacken  an  ordinary  visiting  card  on  one  side,  or 
take  any  smooth,  black,  glossy  piece  of  paper,   and 
holding  a  strong  2O-diopter  convex  lens  close  in  front  of 
it,  reflect  light  through  the  lens  upon  the  card  by  means 
of  a  plane  or  concave  mirror.     By  tilting  or  rotating  the 
mirror,  the  movement  of  the  light  area  (corresponding 
to  the  retinal  illumination)  on  the  card  can  be  studied. 
The  concave  mirror  must  be  at  such  a  distance  that 
the  light  will  have  focused,  or  crossed,  before  reaching 
the  lens.     It  is  possible  to  watch  from  the  side,  and  not 
through  the  lens,  the  movement  of  the  light  area  on  the 
card.     It  is  often  advisable  to  have  an  assistant  tilt  the 
mirror.     The  examiner  may  also  find  it  expedient  to 
place  his  eye  in  the  position  of  the  card,  behind  the  lens, 
while  an  assistant  slightly  tilts  the  mirror.     In  this  way, 
the  differences  between  the  movement  of  the  light  with 
the  plane  and  concave  mirror  may  be  easily  noticed. 
On  removing  the  lens,  it  will  be  interesting  to  note  the 
position  of  the  light  image  in  each  mirror  as  it  is  slowly 
tilted. 

2.  Take  a  black  card  with  a  small  white  spot  in  its 
center,  2  or  3  millimeters  in  diameter;   hold  it  behind  a 


EXPERIMENTS    AND    OBSERVATIONS.  49 

2O-diopter  convex  lens,  which  represents  the  dioptric 
media  of  the  eye,  and  notice  the  apparent  movement, 
position,  size,  etc.,  of  the  image  of  this  white  spot 
through  the  lens,  as  the  card  is  slowly  moved  up  and 
down,  or  from  side  to  side.  This  white  spot  represents 
the  retinal  illumination,  and  its  movement  up  and  down 
or  from  side  to  side  represents  the  movement  of  the  ret- 
inal illumination  when  the  mirrors  are  tilted.  If  a  per- 
fect lens  is  used,  the  observer's  eye  may  be  placed  at  such 
a  distance  in  front  of  it  that  all  the  rays  of  light  passing 
through  it  from  the  white  spot  on  the  card  will  be  fo- 
cused in  his  eye.  If  he  sees  a  large  white  image  of  the 
white  spot  or  a  portion  of  it  filling  the  whole  lens,  he  is 
located  at  the  point  of  reversal,  or  the  anterior  focal 
point  of  the  spot  on  the  card.  If  he  moves  closer  to  the 
lens,  he  can  study  the  conditions  of  emmetropia,  hyper- 
metropia,  and  of  a  low  degree  of  myopia,  where  the 
anterior  focal  point  is  situated  behind  the  examiner, 
the  rays  of  light  not  having  focused  before  reaching 
his  eye.  On  the  other  hand,  if  he  moves  farther  back, 
that  of  a  higher  degree  of  myopia  is  studied  where  the 
anterior  focal  point  is  situated  between  the  card  and  the 
examiner,  the  rays  of  light  having  focused  before  reach- 
ing his  eye.  When  either  in  front  of  or  behind  the  an- 
terior focal  point,  the  examiner  can  move  his  eye  about 
in  different  directions  and  still  see  the  image  of  the  white 
spot  on  the  card.  The  farther  his  eye  is  removed  from 
the  anterior  focal  point,  the  greater  the  space  through 
which  he  can  move  his  eye  and  still  see  the  light  spot. 
The  observer  may  cover  all  dark  or  shady  portions  of 
the  lens  and  still  see  the  image.  But,  if  he  covers  that 
portion  of  the  lens  through  which  the  light  rays  pass  to 
form  this  image,  he  will  hide  it  from  view.  The  white 

6 


50  PHOTOSCOPY. 

spot,  instead  of  being  circular,  may  be  in  the  shape  of  an 
equilateral  triangle,  so  that  it  will  be  easy  for  the  ob- 
server to  know  whether  he  is  looking  at  an  upright  or 
inverted  image  by  noting  the  direction  in  which  the 
apex  of  the  triangle  points. 

The  peripheral  light  ring  seen  in  spherical  aberration, 
having  its  direction  or  rate  of  movement  different  from 
the  movement  of  the  central  light  area,  may  be  well 
studied  with  almost  any  strong  convex  lens.  If  a 
strong  cylindrical  lens  is  held  in  front  of  the  sphere,  the 
bar-like  appearance  of  the  round  white  spot  may  be 
studied  as  in  astigmatism. 

To  demonstrate  that  the  usually  circular-shaped  ret- 
inal illumination  does  not  depend  on  the  shape  of  the 
source  of  light,  reflect  light  from  a  mirror  through  dif- 
ferent shaped  holes  in  a  card  held  close  in  front  of  an- 
other, and  note  that  the  illumination  on  the  second  card 
is  the  same  shape  as  the  holes  in  the  first  card.  The 
perfect  retinal  illumination  would  be  a  mere  point  of 
light.  If  the  light  is  not  focused  soon  enough,  or  too 
soon,  to  form  a  focus  on  the  retina,  diffusion  circles  will 
represent  each  point  of  light  in  the  source.  If  astigma- 
tism is  present,  the  light  will  be  more  nearly  focused  in 
one  chief  meridian  than  in  the  opposite,  making  an 
elliptical  and  sometimes  even  a  linear-shaped  illumina- 
tion. If  the  shape  of  opening  in  the  light  screen  is 
changed,  the  area  of  illumination  thrown  by  any  kind  of 
mirror  held  close  to  the  source  of  light  will  be  similarly 
changed.  If  the  mirror  be  so  far  from  the  source  of 
light  that  it  receives  light  on  every  part  of  it,  the  illu- 
mination caused  by  its  reflection  will  be  the  same  shape 
as  the  mirror. 


CHAPTER  III. 

PRACTICAL  APPLICATION  OF  THE  TEST  WITH  THE 
PLANE  MIRROR.  —  EMMETROPIA.  —  HYPERME- 
TROPIA.  —MYOPIA.— REGULAR  ASTIGMATISM.— 
MIXED  ASTIGMATISM.— IRREGULAR  ASTIGMA- 
TISM. —  POSITIVE  ABERRATION.  —  NEGATIVE 
ABERRATION.  —  CONICAL  CORNEA.  —  CONICAL 
ASTIGMATISM.  —  SCISSORS  APPEARANCE.  —AC- 
COMMODATION.—SUMMARY. 

Practical  Use  of  the  Plane  Mirror.  —  Having 
mastered  and  become  thoroughly  familiar  with  the 
principles  of  photoscopy  as  explained  in  the  preceding 
chapters,  the  student  is  now  ready  to  consider  the  practi- 
cal application  of  the  plane  mirror.  This  method  seems 
to  be  the  simpler,  and  an  understanding  thereof  neces- 
sary, before  attempting  the  explanation  or  use  of  the 
concave  mirror,  for  the  following  reasons : 

1.  It  leads  to  confusion  to  study  two  methods  at  the 
same  time. 

2.  It  is  easier  to  understand  the  principles  of  the  test 
when  the  plane  mirror  is  used. 

3.  The  plane   mirror  is   more  often   useful;    it  can 
practically  be    used  to    the  exclusion  of  the    concave 
mirror. 

4.  Except  in   some   cases   of  myopia,  the   apparent 
source  of  light  and  the  anterior  focal  point  of  the  eye 
can  be  more  nearly  approximated  by  the  plane  than  is 
possible  with  the  concave  mirror.     This  is   always  so 


52  PHOTOSCOPY. 

when  near  the  anterior  focal  point  and  if  the  source  of 
light  is  near  the  mirror.  This  is  indeed  a  very  impor- 
tant desideratum,  because  a  brighter  and  smaller  illu- 
mination on  the  retina  is  obtained;  therefore,  a  more 
distinct  anterior  focal  point. 

A  description  of  the  most  useful  and  common  method 
of  using  the  plane  mirror  can  now  be  considered. 
Some  consideration  of  the  other  methods  in  use  will  be 
given  subsequently. 

1.  The  room  must  be  darkened. 

2.  The  patient  and  examiner  are  to  be  seated  facing 
each  other  at  a  distance  of   I    or  \  meter,  with   their 
eyes  and  the  light  on  the  same  level.     However,  no 
arbitrary  rule  governs  this  distance  between  patient  and 
observer.     The   examiner   may   choose  the   particular 
distance  he  prefers  in  each  individual  case. 

3.  The  source  of  light  should  be  on  the  side  opposite, 
on  the  same  level,  and  at  a  distance  of  5  or  6  inches 
from  the  examiner's  eye  in  use. 

4.  There  should  be  a  5-  or  lo-millimeter  opening  in 
the  light  screen,  opposite  the  brightest  part  of  the  flame, 
thus  permitting  the  central  part  of  the  light  to  pass  in 
front  of  the  examiner's  unused  eye  and  the  shade,  and 
to  fall  upon  the  mirror  held  before  the  other  eye. 

5.  The  mirror  should  be  held  before  the  eye  having 
the  greatest  visual  acuity;  if  the  visual  acuity  of  the  two 
eyes  is  equal,  before  the  right,  if  the  examiner  is  right- 
handed;   before  the  left,  if  left-handed. 

6.  Correcting  lenses  should  be  worn  if  they  improve 
the  examiner's  vision,  which  should  be  at  least  £  for 
good  work.     But  the  fact  must  be  remembered  that 
they  reflect  some  of  the  rays  of  light  which  would  other- 
wise enter  his  eye.     The  examiner  need  take  no  note  of 


3    5- 


PRACTICAL    USE    OF    PLANE    MIRROR.  53 

his  own  accommodation  as  he  is  compelled  to  do  in 
ophthalmoscopy. 

7.  A  trial  frame  should  be  properly  adjusted  on  the 
patient's  face. 

8.  The  trial  lenses  should  be  near  the  examiner,  so 
that  he   can  insert  them  in  the  trial  frame  without 
rising.     (The  writer  has  an  assistant  place  the  required 
lenses  in  the  trial  frame  as  directed.) 

9.  Usually  the  patient's  accommodation  should  be 
overcome  previous  to  the  examination  by  the  use  of  a 
reliable  cycloplegic.     Complete  paralysis  of  the  ciliary 
muscle,    producing   loss   of  the   accommodation,   with 
moderate  dilatation  of  the  pupil,  would  be  the  ideal 
condition,  but  all  drugs  now  in  use  produce  full  dilata- 
tion. 

10.  The  patient's  accommodation  being  thoroughly 
relaxed,  he  should  be  requested  to  look  not  only  directly, 
but  constantly,  at  the  examiner's  brow  just  above  the 
mirror,  or  at  the  dark  edge  of  the  mirror.     In  case  a 
cycloplegic  has  not  been  used  and  the  accommodation 
is  active,  the  patient  should  look  in  a  staring,  absent- 
minded  manner  past  the  brow,  just  above  the  examiner's 
ear,  into  the  distance.     It  is  sometimes  wise,  in  this 
latter  method,  to  place  slightly  fogging  lenses  before  the 
other  eye, — /'.  e.,  a   sufficiently   strong   convex  (+)  or 
weak    concave   ( — )   spherical    lens, — thereby  blurring 
distant  vision.     If  he  looks  directly  at  the  light  in  the 
mirror  the  irritation  sometimes   causes   an  irresistible 
desire   to    close   the   eye,  although   this   is   the  proper 
method  by  which  to  examine  the  macula,  especially  for 
the  spherical  correction.     The  degree  of  astigmatism 
can  often  be  better  told  by  having  the   patient  look, 
during  the   examination   of  both    chief  meridians,   in 


54  PHOTOSCOPY. 

such  a  direction  that  a  bright  reflection  may  be  obtained 
from  the  optic  nerve  ending.  However,  this  would  not 
give  the  proper  spherical  correction.  In  case  of  an 
existing  strabismus,  when  the  squinting  eye  is  under  ex- 
amination, the  other  eye  should  be  covered;  in  fact, 
the  writer  places  a  black  disc  before  the  other  eye  in 
nearly  all  cases. 

11.  It  is  advisable  to  have  a  meter  stick,  marked  in 
dioptric  focal  lengths,  for  determining  the  distance  from 
the  patient's  eye,  as  well  as  marked  in  the  equivalent 
diopters  to  obtain  the  proper  strength  of  concave  ( — ) 
spherical  lens  to  be  added  to  the  dark-room  correction, 
in  allowing  for  working  distance  to  obtain  the  distant 
correction. 

12.  The  handle  of  the  mirror  should  be  held  firmly, 
yet  lightly;  the  mirror  should  reflect  the  central,  bright- 
est rays  of  light  into  the  patient's  eye.     It  takes  both 
patience  and  practice  to  do  this,  or  even  to  keep  the 
light  on  the  face.     The  beginner  is  often  at  a  loss  to 
know  where  the  reflected  light  is,  but  if  he  directs  it  on 
the  unused  hand  held  between  the  mirror  and  the  pa- 
tient's face,  upon  withdrawal  of  the  hand   the    light 
will  be  seen  on  the  patient's  face.      Proficiency  in  the 
control  of  the  mirror  will  soon  be  acquired.     Each  one 
learns  by  practice  the  most  convenient  method  of  holding 
and  manipulating  the  mirror,  possibly  no  two  having 
exactly  the  same  method. 

13.  The  next  step  is  to  tilt  slightly  or  rotate  the  mirror 
about  an  axis  corresponding  to  one  of  its  meridians. 
Unless  these  movements  are  limited  in  range,  the  light 
will  be  lost  from  the  eye.     The  rate  of  movement  de- 
sired, whether  slow  or  fast,  will  be  acquired  in  actual 
practice.     Generally  it  is  best  to  move  the  mirror  slowly. 


PRACTICAL    USE    OF    PLANE    MIRROR.  55 

thus  having  an  opportunity  to  study  the  conditions. 
The  examiner  should  be  certain  of  every  change  in  the 
pupil,  particularly  in  its  central  area,  especially  when 
near  the  anterior  focal  point,  or  if  spheric  aberration 
is  present.  The  writer  has  observed  many  moving  the 
light  up  and  down  the  face  so  fast  that  no  mortal  could 
possibly  tell  in  which  direction  the  light  was  moving  at 
any  one  particular  time,  or  even  recognize  anything  else 
of  importance. 

14.  The  observer  will  next  study  the  light  in  the  pupil. 
This  will  vary  under  different  conditions  as  follows  :- 

(a)  Personal  differences,  due  chiefly  to  varying 
degrees  of  pigmentation  of  the  eye  ground.  In  bru- 
nettes and  mulattoes  it  is  quite  unlike  that  in  blondes 
and  albinos. 

(&)  The  patient  may  turn  the  eye  so  that  the  light  will 
be  reflected  from  different  parts.  The  light  coming 
from  the  nerve  head,  or  an  area  of  retained  nerve  fibers, 
is  quite  different  from  that  emanating  from  a  dark  spot 
or  a  collection  of  pigment  in  the  retina. 

(c )  It  will  vary  in  eyes  of  different  refractive  strengths ; 
and,  of  course,  it  will  be  altered  by  changes  in  the  lenses 
before  the  eye. 

(d)  It  will  be  different  as  the  conditions  change  under 
which  the  examination  progresses, — e.  g.,  the  degree 
of  darkness  in  the  room,  the  relative  position  of  the  ex- 
aminer and  patient,  the  changes  in  the  quality  and 
quantity  of  the  light,  the  distance  between  the  mirror 
and  the  light,  between  the  mirror  and  the  eye,  etc. 

As  a  rule,  however,  a  red  or  orange-colored  glare  or 
glow  fills  the  pupil,  but  the  following  conditions  must 
be  carefully  noted  and  as  far  as  possible  avoided,  as 
otherwise  great  confusion  may  result: 


56  PHOTOSCOPY. 

1 .  Very  small  catoptric  images  of  the  light  or  other  ob- 
jects reflected  by  the  surfaces  of  the  cornea  and  lens  can 
always  be  seen. 

2.  Images  of  the  light,  of  other  objects,  and  even  of 
the  examiner's  face  reflected  by  the  surfaces  of  the  trial 
lens  before  the  eye. 

3.  A  small,  dark  area  due  to  the  perforation  in  the 
mirror  and  more  noticeable  under  certain  conditions 
than  others. 

4.  Frequently   the   outer   portion   of  the    red   glare 
presents  a  bright  ring  of  light,  due  to  the  fact  that  the 
periphery  of  the  lens,  or  cornea,  is  often  of  quite  a  dif- 
ferent refractive  strength  from  the  center,  and  the  rays 
of  light   passing  through  the   periphery  have  focused 
at  the  examiner's  eye,  while  those  through  the  center 
have  not.     However,  the  examiner  is  concerned  only 
with  the  central  portion  of  light.     This  peripheral  light, 
due  to  spherical   aberration,  will  vary  in  width   and 
brightness  as  the  distance  between  the  examiner  and 
patient  is  changed,  or  different  lenses  placed  before  the 
eye.     It  is  the  source  of  more  error,  and  takes  more 

J 

patience  and  practice  to  avoid  than  anything  else  in  the 
test.     (Frontispiece  2  and  3). 

5.  Sometimes  an  image  of  a  hyaloid  artery,  another 
vessel  or  vessels,   masses  of   connective  tissue   some- 
times even  in  the  vitreous,  or  the  nerve  ending,  may  be 
seen.     All  these  may  be  avoided  by  having  the  patient 
look  in  a  slightly  different  direction  from  that  in  which 
these  conditions  were  observed. 

6.  Often  a  very  bright  reflex  is  caused  by  an  improp- 
erly placed  test  lens;  this  can  be  avoided  by  changing 
the  position  of  the  lens. 

The  important  thing  is  a  round,  elliptical,  or  linear- 


EMMETROPIA.  57 

shaped  area,  or  image  of  light,  apparently  moving  in  the 
central  part  of  the  pupil  as  the  mirror  is  tilted.  Rarely 
it  presents  a  smoky,  and  not  the  characteristic  light  ap- 
pearance. It  is  necessarily  small  and  moves  slowly 
when  the  examiner  is  far  from  the  anterior  focal  point  of 
the  eye,  but  becomes  larger,  more  brilliant,  and  moves 
faster  as  he  approaches  it,  and  completely  fills  the  pupil 
when  he  is  at  the  anterior  focal  point.  Success  depends 
on  noticing  the  size,  shape,  brilliancy,  direction,  and  rate 
of  movement  of  the  central  light  area.  Except  when  the 
examiner  is  situated  at  the  anterior  focal  point,  this 
central  light  area  is  always  surrounded  by  a  darker 
portion  which  attends  it  in  all  its  movements,  and  wTere 
it  not  for  the  contrast  or  boundary  between  these  two 
areas,  the  movements  of  the  light  area  could  not  be 
recognized. 

A  convex  (+)  spherical  lens  is  required  when  the 
central  light  area,  or  image,  moves  in  the  same  direction 
as  the  light  on  the  face,  and  indicates  that  the  anterior 
focal  point  is  situated  behind  the  examiner — that  the 
rays  of  light  have  not  focused  before  reaching  his  eye — 
as  in  hypermetropia,  emmetropia,  or  a  low  degree  of 
myopia.  A  concave  ( — )  spherical  lens  is  needed  when 
the  central  light  image  moves  in  an  opposite  direction  to 
the  light  on  the  face,  and  indicates  that  the  anterior 
focal  point  is  situated  between  the  patient  and  examiner, 
in  front  of  the  latter,  as  in  a  higher  degree  of  myopia. 
If  the  light  area,  or  image,  moves  faster  in  one  meridian 
than  in  another,  or  is  shaped  like  a  bar  of  light,  it  indi- 
cates astigmatism,  and  a  cylinder  is  required  in  addition. 

Emmetropia . — As  before  stated,  rays  of  light  pass- 
ing from  an  emmetropic  eye  are  for  all  practical  purposes 
parallel,  forming  a  cylinder  outside  the  eye.  One  end 

7 


58  PHOTOSCOPY. 

of  this  cylinder  rests  in  the  pupil,  the  other  end  at  in- 
finity. When  the  plane  mirror  is  tilted,  the  light  on  the 
face  and  in  the  pupil  moves  in  the  same  direction.  This 
at  once  shows  that  a  plus  lens  in  needed.  If  a  +.88  s. 
lens  be  placed  before  the  eye,  the  central  light  area  is 
larger,  brighter,  moves  faster,  and  in  the  same  direction 
as  before;  but  if  a  -f-i.12  s.  lens  be  used,  the  same 
phenomena  are  observed,  except  that  the  light  in  the 
pupil  moves  in  the  opposite  direction  to  the  light  on  the 


B 

FIG.  14. — Emmetropia  with  the  plane  mirror  tilted  downward  and  the 
concave  upward.  A,  plane  mirror.  B,  concave  mirror.  The  heavy  black 
part  above  represents  that  portion  of  the  mirror  from  which  light  is  re- 
flected to  the  patient's  eyes.  The  retinal  illumination  is  seen  to  be  below 
the  center  of  the  retina.  The  heavy  black  lines  give  the  boundary  of  the 
light  passing  out  of  the  patient's  pupil  in  an  upward  direction.  Only  the 
lower  rays  at  the  examiner's  face  pass  into  his  pupil,  E,  and  if  traced  back 
to  the  patient's  pupil  by  the  dotted  lines  are  seen  to  come  through  the  lower 
part  of  it.  This  lower  part  of  the  pupil  appears  brightly  illuminated  by  the 
central  image,  which  is  projected  between  the  two  dotted  lines  within  the 
eye.  The  pupil  appears  diagrammatically  as  in  L.  The  image  is  erect  as 
the  rays  forming  it  do  not  cross  in  passing  to  the  examiner's  eye.  A  convex 
+ 1 .00  s.  lens  placed  before  such  an  eye  would  cause  all  the  rays  of  light 
emerging  from  the  eye  to  focus  into  the  examiner's  pupil  E,  and  make  the 
patient's  pupil  appear  full  of  light  (Fig.  16.) 

face.  Therefore,  in  the  first  case  the  examiner  was 
within,  in  the  second,  beyond,  the  anterior  focal  point. 
The  lens  whose  strength  is  midway  between  the  two 
will  focus  the  rays  of  light  at  the  examiner's  eye.  It  is 
a  good  plan  in  practice  to  use  two  lenses,  one  pro- 
ducing a  focus  just  beyond,  the  other  just  before  reach- 
ing, the  examiner's  eye.  It  is  better  to  select  the  lens 
whose  strength  is  midway  between  these  two,  as  the 
final  result,  rather  than  attempt  to  find  one  lens  which 


EMMETROPIA.  59 

will  focus  the  rays  of  light  exactly  at  the  examiner's  eye; 
for  it  is  sometimes  very  difficult  to  be  certain  when  at 
the  anterior  focal  point,  but  usually  easy  to  know  when 
beyond  or  within  it. 

In  the  above  example,  if  the  examiner  is  working  at 
one  meter  distance,  a  -f  i.oo  s.  lens  would  be  the  final 
result  for  that  distance,  and  by  adding  a  — i.oo  s.  lens 
as  the  allowance  for  working  distance  (see  pp.  87,  88 
89),  the  +1.00  s.  would  be  neutralized  and  no  lens 
would  be  necessary  for  the  distance. 

If  the  examiner  should  place  a  lens  in  front  of  the 


\ 


\( 

A  B 


FIG.  15. — Emmetropia  with  the  plane  mirror  tilted  upward  and  the 
concave  downward.  A,  plane  mirror.  B,  concave  mirror.  The  retinal  illu- 
mination is  seen  to  be  above  the  center  of  the  retina.  The  heavy  black 
lines  give  the  boundary  of  the  light  passing  out  of  the  patient's  pupil  in  a 
downward  direction.  Only  the  upper  rays  of  the  area  of  light  at  the  ex- 
aminer's face  pass  into  the  examiner's  pupil  E,  and  if  traced  back  to  the 
patient's  pupil  by  the  dotted  lines  are  seen  to  pass  through  the  upper  part 
of  it.  This  upper  part  of  the  pupil  appears  brightly  illuminated  by  the 
image  which  is  projected  between  the  two  dotted  lines  within  the  eye.  The 
pupil  appears  diagramrnatically  as  in  L.  The  image  is  erect  because  the 
rays  forming  it  do  not  cross  in  passing  to  the  observer's  eye. 


patient's  eye  that  focuses  the  rays  of  light  at  his  own  eye, 
no  movement  of  the  central  light  area  being  noticeable, 
by  first  moving  forward  and  then  backward,  the  dif- 
ference in  direction  in  which  the  light  moves  in  each 
position  determines  whether  he  is  within  or  without  the 
focal  point.  The  focal  point  is  between  these  two 
positions.  When  the  examiner  moves  backward,  the 
central  light  area,  or  image,  will  move  in  an  opposite 
direction  to  the  light  on  the  face,  and  when  he  moves 


60  PHOTOSCOPY. 

forward,  it  will  move  in  the  same  direction  as  the  light 
on  the  face  (Figs.  14,  15,  and  16). 

Particular  attention  should  be  given  to  the  central 
light  area,  and  as  far  as  possible  the  confusing  periph- 
eral light  areas  due  to  aberration  should  be  avoided. 
(See  Positive  and  Negative  Aberration,  pp.  73,  75.) 


f 


FIG.  1 6.  —  The  examiner's  eye  at  the  anterior  focal  point  of  an  eye: 
Emmetropia,  hypermetropia,  or  a  low  degree  of  myopia  with  the  correcting 
convex  spherical  lens  before  the  eye.  The  rays  of  light  passing  from  the 
retinal  illumination  out  of  the  observed  pupil  are  focused  by  the  lens  L 
into  the  examiner's  pupil  E,  as  seen  by  the  dotted  lines,  and  therefore  the 
observed  pupil  appears  to  be  filled  with  light  (a  magnified  image  of  all  or 
part  of  the  retinal  illumination)  as  represented  diagrammatically  in  C. 
No  image  of  the  darker  portion  of  the  retina  is  formed  in  an  eye  which 
has  equal  refractive  strength  through  all  parts  of  its  pupil  since  al!  the 
rays  will  then  focus  in  the '  examiner's  pupil  which  otherwise  they  will 
not  do. 

If  a  concave  ( — )  replaced  the  convex  (-f-)  lens  in  this  diagram  before 
an  eye  having  a  high  degree  of  myopia  focusing  all  the  rays  of  light  passing 
from  the  retinal  illumination  into  the  examiner's  pupil  E,  it  would  represent 
diagrammatically  the  examiner  at  the  anterior  focal  point  of  a  more  myopic 
eye. 

This  diagram  also  represents  the  examiner's  eye  at  the  anterior  focal 
point  of  the  vertical  meridian  (ax.  90)  of  an  eye. 

Hypermetropia. — In  examining  a  hypermetropic 
eye  by  this  method,  it  is  necessary  to  remember  that  the 
light  rays  passing  out  of  such  an  eye  form  a  truncated 
cone  (Fig.  83),  its  smaller  end  filling  the  pupil,  the 
larger  end  resting  at  infinity,  or,  for  practical  purposes, 
at  the  examiner's  face. 

The  size  of  the  larger  end  of  this  cone  at  the  ex- 
aminer's face  depends  on  the  distance  of  the  examiner 
and  the  amount  of  hypermetropia  present,  and  chiefly 
determines  the  size,  shape,  brilliancy,  and  rate  of  move- 
ment of  the  central  light  area  in  the  patient's  pupil. 


HYPERMETROPIA. 


6l 


The  central  light  area  moves  in  the  same  direction  as  the 
light  on  the  face;  therefore,  a  convex  (+)  lens  is  needed. 
The  same  procedure  now  is  followed  as  first  described  in 


A  B 

FIG.  17. —  Hypermetropia  with  the  plane  mirror  tilted  downward  and 
the  concave  upward.  A,  plane  mirror.  B,  concave.  The  retinal  illumi- 
nation is  seen  to  be  below  the  center  of  the  retina.  The  heavy  black  lines 
give  the  boundary  of  the  light  passing  out  of  the  patient's  pupil  in  an  up- 
ward direction.  Only  the  lower  rays  at  the  examiner's  face  pass  into  his 
pupil  E,  and  if  traced  back  to  the  patient's  pupil  by  the  dotted  lines  are 
seen  to  come  through  the  lower  part  of  it.  This  lower  part  of  the  pupil  ap- 
pears brightly  illuminated  by  the  image,  which  is  projected  between  the  two 
dotted  lines  within  the  eye.  The  pupil  appears  diagrammatically  as  in  L. 
The  image  is  erect  since  the  rays  do  not  cross  in  passing  to  the  examiner's  eye. 


V 


A  B 


FIG.  18. — Hypermetropia  with  the  plane  mirror  tilted  upward  and  the 
concave  downward.  A,  plane  mirror.  B,  concave  mirror.  The  heavy  black 
part  below  represents  that  portion  of  the  mirror  from  which  the  light  is  re- 
flected to  the  patient's  eye.  The  retinal  illumination  is  seen  to  be  above 
the  center  of  the  retina.  The  heavy  black  lines  give  the  boundary  of  the 
light  passing  out  of  the  patient's  pupil  in  a  downward  direction.  Only  the 
upper  rays  of  the  area  of  light  at  the  examiner's  face  pass  into  the  exam- 
iner's pupil  E,  and  if  traced  back  to  the  patient's  pupil  by  the  dotted  lines 
are  seen  to  come  through  the  upper  part  of  it.  This  upper  part  of  the  pupil 
appears  brightly  illuminated  by  the  image  which  is  projected  between  the 
two  dotted  lines  within  the  eye.  The  pupil  appears  diagrammatically  as 
in  L.  The  image  is  erect  because  the  rays  forming  it  do  not  cross  in  passing 
to  the  observer's  eye. 


emmetropia.     Two  lenses  are  selected,  each  producing 
a  light  area  in  the  pupil  of  the  same  size,  shape,  bril- 


62  PHOTOSCOPY. 

liancy,  and  rate  of  movement,  except  that  in  one  the 
central  light  area  in  the  pupil  moves  with,  and  with 
the  other  against,  the  light  on  the  face.  The  lens 
whose  strength  is  midway  between  the  two  used 
will  be  the  final  result.  If  the  size,  shape,  brilliancy, 
and  rate  of  movement  with  a  4-1-75  s.  placed  before 
the  eye  is  the  same  as  with  a  +2.25  s.,  but  with 
the  +1.75  s.  the  central  light  in  the  pupil  moves  with, 
and  with  the  4-2.25  s.  against,  the  light  on  the 
face,  a  4-2.00  s.  lens  will  be  the  final  result  for  I 
meter;  and,  by  adding  a  — i.oo  s.  as  the  allowance  for 
working  distance,  the  4-I.OO  s.  that  remains  is  the  re- 
sult for  the  distance.  The  examiner,  by  moving  within 
and  without  the  anterior  focal  point  just  referred  to — 
i.  <?.,  closer  to,  or  farther  from,  the  patient  than  this 
point — can  locate  its  exact  position  and  is  thus  enabled 
to  determine  the  correction  for  distance  (Figs.  17  and 

18). 

Myopia  (Hypometropia) . — Rays  of  light  returning 
from  the  retina  of  a  myopic  eye  pass  out  and  form  a  cone 
whose  apex  is  at  the  anterior  focal  point  and  whose  base 
corresponds  to  the  pupil  of  the  eye  (Fig.  82).  If  noth- 
ing obstructs  the  light  at  its  anterior  focal  point  the 
rays  will  cross  and  pass  on,  forming  another  cone,  its 
apex  touching  the  apex  of  the  first  cone,  its  base  at  in- 
finity. Two  cones  are  thus  formed.  The  examiner's 
eye  will  either  be  at  the  apex  (anterior  focal  point)  or 
in  one  of  the  cones.  If  at  the  apex  (the  anterior  focal 
point  of  the  eye)  the  examiner  will  have  all  the  signs  to 
indicate  it, — viz.,  the  pupil  filled  by  central  light  area, 
not  movable,  etc.  If  in  the  first  cone,  or  closer  to  the 
eye  than  its  anterior  focal  point,  the  same  signs  will  be 
present  as  in  emmetropia  and  hypermetropia, — i.  e.y 


MYOPIA  (HYPOMETROPIA).  63 

light  moving  with  the  light  on  the  face,  and  convex  (+) 
spherical  lenses  should  be  used  until  the  focal  point  and 
the  examiner's  eye  coincide.  By  adding  a  — i.oo  s.  to 
the  result,  if  working  at  one  meter,  the  correction  for 
distance  will  be  obtained.  If  the  examiner  is  beyond 
the  anterior  focal  point,  and  thus  in  the  second  cone,  the 
central  light  area  in  the  pupil  will  move  opposite  to  the 
light  on  the  face,  and  concave  ( — )  spherical  lenses  will 
be  needed.  Pursuing  the  same  method  as  in  the  former 


FIG.  19. — Myopia  with  the  plane  mirror  tilted  downward  and  the  con- 
cave upward.  A,  plane  mirror.  B,  concave  mirror.  The  retinal  illumina- 
tion is  seen  to  be  below  the  center  of  the  retina.  The  heavy  black  lines  give 
the  boundary  of  the  light  passing  out  of  the  patient's  pupil  in  an  upward 
direction.  The  light  rays  are  seen  to  focus  and  cross  at  F;  only  the  lower 
rays  at  the  examiner's  face  pass  into  his  pupil  E,  and  if  traced  back  to  the 
patient's  pupil  by  the  dotted  lines  are  seen  to  come  through  the  upper  part 
of  it,  having  crossed  at  F.  This  upper  part  of  the  pupil  appears  brightly 
illuminated  by  the  image  which  is  projected  between  the  two  dotted  lines 
within  the  eye.  The  pupil  appears  diagrammatically  as  in  L.  The  image 
is  inverted,  the  rays  forming  it  having  crossed  in  passing  to  the  examiner's 
eye. 

conditions  already  considered,  two  lenses  are  selected, 
one  producing  a  focus  of  the  light  just  beyond,  the  other 
just  before  reaching  the  examiner's  eye.  Therefore, 
to  produce  a  focus  at  the  examiner's  eye,  it  is  necessary 
to  select  a  lens  whose  strength  is  midway  between  the 
two.  To  find  the  correction  for  distance,  a  — i.oo's. 
must  be  added  if  working  at  one  meter  distance, — e.  g., 
if — 2.00  s.  be  the  correction  for  one  meter  adding — i.oo 
s.,  the  result,  — 3.00  s.,  is  the  correction  for  distance. 
It  is  also  possible  to  find  the  location  of  the  anterior 


64  PHOTOSCOPY. 

focal  point  by  moving  closer  to,  or  farther  from,  the 
patient's  eye,  and  thus  determine  the  degree  of  myopia 
present  (Figs.  19  and  20). 

Regular  Astigmatism. —  In  regular  astigmatism 
the  rays  of  light  form  neither  a  cylinder  nor  a  perfect 
or  truncated  cone  outside  the  eye,  because  rays  passing 
through  one  chief  meridian  will  focus  at  a  greater  or 
less  distance  from  the  eye  than  those  passing  through 
the  meridian  at  right  angles.  Those  through  one  me- 


A  B 


FIG.  20. — Myopia  with  the  plane  mirror  tilted  upward  and  the  concave 
downward.  A,  plane  mirror.  B,  concave  mirror.  The  heavy  black  part 
below  represents  that  portion  of  the  mirror  from  which  the  light  is  reflected 
to  the  patient's  eye.  The  retinal  illumination  is  seen  to  be  above  the  center 
of  the  retina.  The  heavy  black  lines  give  the  boundary  of  the  light  passing 
out  of  the  patient's  pupil  in  a  downward  direction.  The  light  rays  are  seen 
to  focus  and  cross  at  F.  Only  the  upper  rays  at  the  examiner's  face  pass 
into  his  pupil  E,  and  if  traced  back  to  the  patient's  pupil  by  the  dotted  lines, 
are  seen  to  come  through  the  lower  part  of  it,  having  crossed  at  F.  This 
lower  part  of  the  pupil  appears  brightly  illuminated  by  the  image  which  is 
projected  between  the  two  dotted  lines  within  the  eye.  The  pupil  appears 
diagrammatically  as  in  L.  The  image  is  inverted,  the  rays  forming  it  hav- 
ing crossed  in  passing  to  the  examiner's  eye. 

ridian  will  be  more  or  less  divergent,  or  convergent,  than 
those  through  the  opposite.  In  other  words,  the  refrac- 
tive power  of  one  of  the  two  chief  meridians  is  stronger, 
or  weaker,  than  that  of  the  opposite  meridian.  In  this 
form  of  astigmatism  the  examiner  is  concerned  in  de- 
termining the  position  of  the  anterior  focal  point  in  only 
the  strongest  and  weakest  meridians.  It  is  therefore 
necessary  to  determine  in  which  direction  each  me- 
ridian lies.  The  meridian  whose  anterior  focal  point  is 
nearest  the  examiner's  eye  will  appear  more  nearly  full 


REGULAR   ASTIGMATISM.  65 

of  light  than  the  opposite,  because  the  examiner's  eye 
receives  more  of  the  rays  of  light  which  pass  through 
that  meridian  than  through  the  other.  The  central 

O 

light  area  has  more  or  less  the  appearance  of  a  bar, 
and  the  more  nearly  it  fills  a  meridian,  the  nearer  the 
examiner's  eye  is  to  the  anterior  focal  point  of  that  me- 
ridian. In  other  words,  the  length  of  the  bar  lies  in  the 
more  nearly  corrected  meridian,  and  the  direction  of  its 
movement  endways  determines  whether  a  convex  (  +  ) 
or  a  concave  ( — )  spherical  lens  is  needed.  When  the 
anterior  focal  point  of  a  meridian  and  the  examiner's 
eye  coincide,  the  bar  of  light  extends  entirely  across  the 
pupil  in  that  meridian.  If  in  such  a  case  the  degree  of 
astigmatism  is  low,  the  width  of  the  bar  of  light  will 
be  much  greater  than  if  it  is  high;  for  in  a  low  degree  of 
astigmatism  the  anterior  focal  points  of  the  two 
principal  meridians  are  not  widely  separated;  the 
examiner's  eye  receives  all  the  rays  of  light  from  the 
meridian  corresponding  to  the  length  of  the  bar,  and 
nearly  all  from  the  one  corresponding  to  the  width.  In 
a  high  degree  of  astigmatism,  the  anterior  focal  points 
are  widely  separated,  and  the  examiner's  eye,  while 
receiving  the  rays  of  light  from  one  meridian,  receives 
only  a  small  number  of  the  rays  from  the  opposite 
meridian.  It  will  be  seen  that  the  degree  of  astigma- 
tism is  the  difference  between  the  refractive  strengths 
of  the  two  chief  meridians,  or  it  is  the  difference  be- 
tween the  distances  of  their  two  anterior  focal  points 
from  the  eye  expressed  in  focal  lengths.  In  other  words, 
it  is  the  strength  of  the  lens  which  will  move  either 
anterior  focal  point  to  the  other.  This  can  be  done 
by  a  plus  lens,  which  will  shorten  the  distance  of  the 
farther  focal  point,  or  by  a  minus  lens,  which  will  ex- 


66  PHOTOSCOPY. 

tend  the  distance  of  the  nearer  one,  until  the  two  coin- 
cide. The  bar  of  light  is  always  seen  in  one  of  the 
chief  meridians,  and  the  mirror  should  be  tilted  so 
that  the  light  moves  in  or  along  this  meridian  (up  and 
down  if  at  axis  90,  from  side  to  side  if  at  axis  180). 
This  meridian  should  be  corrected  before  proceeding 
to  the  correction  of  the  opposite,  because  it  is  better 
in  practice  to  correct  each  meridian  separately,  using 
the  methods  already  described  under  myopia  and  hyper- 
metropia  (Fig.  21  and  Frontispiece  4,  5,  and  6). 


B 

FIG.  21. — Regular  astigmatism.  A,  plane  mirror.  B,  concave  mirror. 
The  heavy  black  lines  indicate  the  boundary  of  the  rays  passing  out  of  the 
pupil  through  the  vertical  meridian  (ax.  90°).  Only  that  portion  of  these 
rays  included  between  the  two  dotted  lines  enter  the  examiner's  pupil  E. 
The  fine  black  lines  represent  the  rays  passing  out  of  the  pupil  through  the 
horizontal  meridian  (ax.  180°),  and  they  are  seen  to  focus  in  the  examiner's 
pupil  E.  Since  all  the  rays  passing  out  of  the  pupil  of  the  eye  in  the  hori- 
zontal meridian,  but  only  the  central  ones  in  the  vertical  meridian,  enter  the 
examiner's  eye,  the  horizontal  meridian  of  the  pupil  appears  full  of  light, 
but  only  the  central  part  of  the  vertical  meridian.  This  gives  rise  to"  the 
bar-like  appearance  across  the  pupil  as  seen  in  L.  The  dotted  lines  within 
the  eye  give  the  position  of  the  image  of  light  as  it  is  projected  within  the 
eye  in  the  vertical  meridian. 

The  examiner  must  remember  that  he  is  always  re- 
fracting the  meridian  in  the  direction  in  which  or  along 
which  he  moves  the  mirror  (this  is  not  ophthalmoscopy). 
He  should  move  the  mirror  so  that  the  light  will  move 
along  in  the  direction  of  the  bar  of  light,  thus  making 
the  bar  of  light  move  endways  until  it  ceases  to  move,  or 
extends  completely  throughout  the  meridian  in  which 
it  lies.  It  is  wise  to  find  a  lens  with  which  it  moves 
slightly  with,  then  another  with  which  it  moves  slightly 


REGULAR   ASTIGMATISM.  67 

against,  the  light  on  the  face.  The  lens  in  strength 
between  these  two  will  correct  that  meridian. 

Thus,  if  in  a  given  case  with  a  +.75  s.  the  light  moves 
with,  and  with  a  +1.25  s.  against,  in  the  vertical  me- 
ridian (axis  90°),  the  correction  for  that  meridian  would 
be  a  +1.00  s.  The  bar  of  light  will  now  extend  en- 
tirely across  the  pupil  in  that  meridian.  By  the  same 
method,  the  correction  for  the  opposite  horizontal  me- 
ridian may  be  found  to  be  a  +2.00  s.,  causing  the  bar  of 
light  to  extend  across  the  pupil  in  that  meridian.  The 
amount  of  astigmatism  is  equal  to  the  difference  in 
strength  between  the  two  lenses  necessary  for  the 
correction  of  each  meridian,  which  is  +1.00  c.  The 
correction  for  one  meter  distance  will  be  +1.00  s.  O  + 
i.oo  c.  axis  90°.  The  distant  correction  needed  would 
be  +  1.00  c.  axis  90°.  (See  General  Considerations.) 

The  great  majority  of  eyes  having  astigmatism  also 
require  some  spherical  correction.  In  such  cases  it  is 
necessary  to  place  convex  (  +)  or  concave  ( — )  spheres 
before  the  eyes  until  the  examiner  is  close  to  the  anterior 
focal  point  of  one  of  the  meridians,  when  the  bar  of 
light  will  be  more  clearly  seen  extending  in  that  me- 
ridian. It  is  sometimes  best  in  correcting  high  degrees 
of  astigmatism  to  use  a  sphere  and  a  cylinder  in  com- 
bination, the  sphere  correcting  one,  and  the  two  com- 
bined the  opposite  meridian.  A  sphere  is  found  which 
corrects  one  meridian — e.  g.,  axis  90° — then  different 
cylinders  are  placed  at  the  same  axis  (90) — since  the 
strength  of  a  cylinder  is  at  right  angles  to  its  axis — until 
the  opposite  meridian  is  likewise  corrected.  Many  do 
this  as  a  routine  practice,  but  it  takes  much  time  and 
great  care  to  place  cylinders  at  the  right  axes,  especially 
in  a  dark  room.  Except  in  certain  cases,  the  writer 


68  PHOTOSCOPY. 

much  prefers  to  correct  each  meridian  separately  with 
a  sphere.  It  is  often  advisable  to  prove  the  result  with 
the  sphere-cylinder  combination,  making  the  anterior 
focal  points  of  both  principal  meridians  coincide  in 
position  with  the  examiner's  eye. 

Experience  frequently  enables  the  examiner  to  de- 
termine the  degree  of  astigmatism  present  by  observing 
the  rate  of  movement  of  the  light  area  in  one  of  the 
principal  meridians  after  the  other  is  corrected  by  a 
sphere — if  slow,  a  strong,  if  fast,  a  weak  cylinder  is 
required — and  also  by  observing  the  characteristics  of 
the  bar  of  light.  Cases  with  a  low  degree  of  astigma- 
tism may  often  be  detected  by  a  faint  shaded  area  on 
each  side  of  the  bar  of  light  (Frontispiece  6),  and  also 
by  noting  with  the  correct  sphere  (or  one  slightly  too 
strong  or  too  weak)  if  there  is  any  movement  in  one  of 
the  meridians  while  the  opposite  meridian  appears  cor- 
rected, or  if  the  movement  is  more  distinct  in  one  than 
in  the  other  meridian.  Great  care  must  be  exercised 
in  these  cases,  and,  when  in  doubt,  it  is  often  advisable 
to  increase  or  decrease  the  correcting  sphere,  as  it  is 
usually  possible  with  one  or  the  other  to  notice  a  more 
distinct  movement  in  one  of  the  chief  meridians  than  in 
the  opposite  meridian. 

If  there  is  a  high  degree  of  astigmatism,  in  a  case  re- 
quiring only  a  weak  sphere  to  correct  one  meridian,  the 
bar  of  light  will  be  recognized  on  first  inspection  of  the 
reflex;  but,  if  the  astigmatism  is  low  in  degree  and  a 
strong  sphere  is  required  for  the  high  degree  of  hyper- 
metropia  or  myopia  present,  the  bar  of  light  will  not  be 
recognized  until  a  strong  sphere  corrects,  or  nearly 
corrects,  one  of  the  meridians. 

As  pointed  out  by  my  brother,  Dr.  David  W.  Steven- 


REGULAR    ASTIGMATISM.  69 

son,  of  Richmond,  Indiana,  astigmatism  is  caused  en- 
tirely by  the  anterior  refractive  surfaces  and  media. 
Theoretically,  in  order  to  determine  the  proper  sphere, 
the  illuminated  area  on  the  patient's  retina  should  lie 
on  its  central,  most  important  part,  the  macula,  the  pa- 
tient being  directed  to  look  at  the  light  image  in  the 
mirror.  This  portion  of  the  retina  is  usually  dark  and 
reflects  the  light  poorly  to  the  examiner's  eye.  During 
the  examination  for  astigmatism,  if  the  patient  looks 
steadily  in  such  a  direction  that  the  light  will  be  re- 
flected by  a  certain  part  of  the  bright  optic  nerve  ending, 
it  is  sometimes  easier  to  determine  the  degree  of  astigma- 
tism on  account  of  the  brighter  illumination.  If  the 
illuminated  area  at  the  back  of  the  eye  remains  in  the 
same  location  and  the  proper  sphere  is  determined  to 
correct  each  of  the  two  chief  meridians,  the  difference 
in  strength  between  the  correcting  spheres  for  the  two 
meridians  will  be  equal  to  the  degree  of  astigmatism. 
In  order  to  determine  the  proper  spherical  correction, 
the  illumination  on  the  retina  should  be  at  the  macula, 
but  the  optic  nerve  ending  or  any  other  bright  part  of 
the  fundus  may  be  used  in  determining  the  degree  of 
astigmatism,  which  depends  merely  upon  the  difference 
in  curvature  of  the  two  chief  meridians  of  the  anterior 
refractive  surfaces. 

If  the  light  from  the  mirror  is  not  moved  along  one  of 
the  principal  meridians,  when  astigmatism  is  present 
the  bar  of  light  seems  to  move  in  a  direction  different 
from  that  in  which  it  really  does  move.  This  may  be 
explained  by  passing  a  card,  the  edge  of  which  is  held  at 
an  angle  of  45°,  horizontally  across  and  behind  a 
small  round  opening  in  a  larger  card.  The  edge  of 
the  card  will  appear  to  be  moving  in  a  slanting  direc- 


7O  PHOTOSCOPY. 

tion  instead  of  horizontally.  So  if  a  slanting  bar  of 
light  is  moved  horizontally  across  the  pupil,  or  up  and 
down,  it  will  appear  to  be  moving  in  a  slanting  direction 
at  right  angles  to  its  length  instead  of  in  the  direction  in 
which  it  is  really  moved. 

Mixed  Astigmatism. — This  being  a  form  of  regular 
astigmatism  it  is  dealt  with  in  an  exactly  similar  manner. 
One  of  the  chief  meridians  is  first  corrected  by  a  sphere, 
the  light  being  moved  along  that  meridian;  then  the 
sphere  is  found  that  corrects  the  meridian  at  right  angles. 
The  results  should  be  properly  recorded  on  the  cross 
(Fig.  21  and  Frontispiece  4,  5,  and  6). 

Irregular  Astigmatism. — In  an  ideal  standard,  a 
so-called  emmetropic  or  a  typical  hypermetropic  or 
myopic  eye,  all  the  areas  of  the  pupil  will  have  exactly 
the  same  refractive  strength,  and  all  meridians  will  have 
exactly  the  same  strength.  Likewise  every  part  of  each 
meridian  will  be  alike.  In  practice  such  eyes  are  never 
found.  Every  eye  has  either  slight  or  marked  dif- 
ferences in  the  refractive  strength  in  its  different  pupil- 
lary areas.  This  is  due  to  irregularities,  first,  in  the 
surfaces;  second,  to  differences  in  the  density  of  the 
different  portions  of  one  or  more  of  its  media.  The 
difference  in  the  refractive  strength  of  the  different 
areas  of  the  lens  is  due  to  irregularities  of  its  surfaces, 
and  partly  to  the  fact  that  the  individual  lens  fibers  are 
not  alike  in  shape,  arrangement,  or  density.  The 
slight  differences,  which  always  exist,  give  rise  to  the 
appearance  of  radiations  passing  from  the  edge  of 
stars,  or  distant  lights;  but  changes  in  the  lens  occurring 
during  the  formation  of  cataract,  sometimes  congeni- 
tal, are  gross  enough  to  cause  much  annoyance. 
Usually  these  spicules,  or  lens  opacities,  which  are  seen 


IRREGULAR   ASTIGMATISM.  Jl 

as  shadows  or  dark  lines,  extend  from  the  periphery 
toward  the  center  (Frontispiece  n).  So  long  as  they 
do  not  encroach  on  the  pupillary  area  (which  changes 
as  the  degree  of  light  and  accommodation  varies,  caus- 
ing contraction  or  dilatation  of  the  pupil),  they  do  not 
interfere  with  vision.  Often  they  cannot  be  recognized 
with  the  opthalmoscope,  and  not  even  with  the  photo- 
scope,  unless  the  pupil  is  dilated  and  the  observer  is  near 
the  anterior  focal  point.  The  early  recognition  of  these 
changes  is  important  from  the  prognostic  and  pro- 
phylactic standpoints,  indicating  local  or  general  treat- 
ment, a  change  of  occupation,  eye  rest,  or  the  use  of 
proper  lenses,  especially  if  there  is  astigmatism  against 
the  rule,  or  at  an  oblique  axis  (Frontispiece  II  and  12). 

The  cornea  ought  to  have  both  surfaces  curved  so 
regularly  that  every  part  of  each  meridian  would  have 
the  same  curvature,  and  that  every  meridian  would  be 
like  every  other  meridian.  If  two  meridians  at  right 
angles  have  not  the  same  degree  of  curvature,  and  all 
meridians  in  between  them  gradually  equalize  the 
difference,  then  there  is  regular  astigmatism.  But 
when  there  are  surface  irregularities,  differences  in  the 
curvature  of  different  parts  of  one  meridian,  so  that  one 
area  focuses  at  one  place,  and  another  bearing  a  par- 
ticular relationship  to  this  one  focuses  at  another  place, 
there  is  irregular  astigmatism. 

Distinct  areas  of  light  and  of  darkness  will  be  noticed, 
especially  upon  approaching  the  anterior  focal  point. 
The  reason  for  this  is  that  the  rays  passing  through  the 
light  areas  enter  the  observer's  eye,  but  those  through 
the  dark  areas  do  not. 

The  same  methods  should  be  used  in  the  examination 
and  correction  of  these  cases  as  have  been  described  for 


72  PHOTOSCOPY. 

those  already  considered.  However,  the  examiner 
should  be  careful  to  confine  his  attention  as  much  as 
possible  to  the  central  portion  (easy  to  say,  but  dif- 
ficult to  do)  which  corresponds  to  the  normal  pupil, 
observing  at  all  times  the  movement  of  the  central  light 
only,  avoiding  the  smaller  confusing  areas  of  light  and 
darkness.  Often,  to  obtain  the  best  results,  these 
cases  should  be  examined  not  only  before  and  during 
the  influence  of  a  cycloplegic  but  also  afterward  by  sub- 
jective methods.  (The  axes  of  corneal  and  lenticular 
astigmatism  do  not  always  lie  in  the  same  meridian  nor 
at  right  angles  to  each  other.  This  condition  might 
well  be  termed  crossed  astigmatism  and  is  probably 
more  frequent  than  generally  supposed  because  of  dif- 
ficulty of  detection.  Certain  other  atypical  types  of 
astigmatism  due,  e.  g.y  to  a  combination  of  corneal  astig- 
matism with  lenticular  inclination,  may  also  be  termed 
crossed  astigmatism.) 

Positive  Aberration.— This  is  a  condition  in  which 
rays  of  light  passing  through  the  periphery  of  each  me- 
ridian of  a  spherical  refractive  medium  focus  nearer  it 
than  those  passing  through  its  center.  This  is  due  to 
the  fact  that  the  peripheral  has  greater  refractive  strength 
than  the  central  portion.  This  condition  is  the  most 
frequent  cause  of  the  annoyances  in  photoscopy.  The 
examiner  is  interested  only  in  finding  the  correction  of 
the  central  area,  and  not  that  of  the  periphery,  for 
when  the  pupil  contracts  after  the  effects  of  the  cyclo- 
plegic have  disappeared  the  central  area  only  is  used. 
When  the  examiner  is  within  the  anterior  focal  points 
of  both  the  central  and  peripheral  portions  of  a  given 
meridian,  both  the  central  and  peripheral  light  in  the 
pupil  will  move  in  the  same  direction  as  the  light  on 


POSITIVE    ABERRATION.  73 

the  face;  but,  as  the  examiner  comes  nearer  the  focus 
of  the  peripheral  than  of  the  central  rays,  the  peripheral 
band  of  light  will  appear  more  brilliant  and  move  faster 
than  the  central  area.  A  convex  (  +)  spherical  lens  is 
needed,  and,  if  a  convex  lens  is  already  before  the 
eye,  a  stronger  one;  but  a  weaker  one  if  a  concave  has 
been  used. 

When  the  examiner  is  between  the  focal  points  of  the 
central    and   peripheral   rays,   the   peripheral    band   of 


8 


FIG.  22. — Positive  aberration.  The  peripheral  rays  of  light  passing 
through  this  lens  are  seen  to  focus  at  A,  before  those  passing  through  the 
more  central  part,  which  focus  at  B.  If  the  examiner's  pupil  were  located 
at  A,  the  whole  periphery  would  be  occupied  with  a  band  of  light,  whereas 
the  more  central  area  would  be  occupied  by  a  dimmer  central  image  moving 
with  the  light  on  the  face  (with  a  plane  mirror).  If  the  examiner's  eye  were 
located  at  B,  the  central  part  of  the  pupil  would  be  brightly  illuminated  and 
there  would  be  a  band  of  light  in  the  peripheral  area  moving  against  the 
light  on  the  face  (with  the  plane  mirror).  If  the  examiner  were  located  mid- 
way between  A  and  B,  there  would  be  a  peripheral  and  central  area  of  light 
moving  at  the  same  rate  in  opposite  directions  (with  plane  or  concave  mir- 
rors). If  the  examiner  be  located  beyond  B,  both  central  and  peripheral 
areas  of  light  would  move  against  the  light  on  the  face,  but  the  central  area 
would  move  more  rapidly  (with  the  plane  mirror).  If  the  examiner's  eye 
be  located  closer  to  the  lens  than  A,  both  central  and  peripheral  areas  would 
move  with  the  light  on  the  face,  but  the  peripheral  area  would  move  faster 
and  be  more  brightly  illuminated  (with  the  plane  mirror). 

light  will  move  against  the  light  on  the  face,  while  the 
central  area  will  still  move  with  the  light  on  the  face. 
The  peripheral  band  of  light  and  the  central  light  area 
are  apt  to  encroach  upon  each  other,  and  their  rel- 
ative brilliancy  and  rate  of  movement  depend  on  the 
position  of  the  examiner's  eye  between  their  focusing 
points.  The  pupil  may  appear  full  of  light,  and  this 
often  leads  the  examiner  to  think  wrongly  he  is  at  the 
anterior  focal  point;  the  peripheral  light  moving 

9 


74  PHOTOSCOPY. 

against  may  lead  him  to  believe  wrongly  he  is  beyond  the 
anterior  focal  point,  and  thus  in  need  of  a  concave  ( — ) 
spherical  lens;  or,  if  a  lens  is  already  before  the  eye, 
a  weaker  if  convex,  and  a  stronger  if  concave. 

This  confusing  appearance  is  the  most  frequent 
source  of  error  with  which  the  photoscopist  has  to 
contend.  In  order  to  overcome  this  annoyance,  he 
should  ignore  the  peripheral  and  confine  the  attention 
entirely  to  the  central  light  area,  which  will  be  seen  to 
move  with  the  light  on  the  face  (this,  however,  is  dif- 
ficult and  sometimes  almost  impossible  to  do).  A 
convex  (  +)  spherical  lens  is  needed,  and  if  a  lens  is  al- 
ready before  the  eye,  a  stronger  convex,  if  a  convex; 
and  a  weaker  concave,  if  a  concave. 

When  the  examiner  is  beyond  both  focal  points,  the 
peripheral  band  and  central  light  areas  move  against 
the  light  on  the  face,  the  central  being  more  brilliant 
and  moving  faster  than  the  peripheral.  For  this,  a 
concave  ( — )  spherical  lens  is  required.  If  a  lens  is 
already  before  the  eye,  a  weaker  if  convex,  and  a 
stronger  if  concave  (Frontispiece  2  and  3). 

Photoscopy  is  of  great  value  in  these  cases,  especially 
when  there  is  a  high  degree  of  aberration.  In  these, 
subjective  examinations  are  sometimes  misleading,  as 
the  patient  with  a  dilated  pupil  may  choose  correcting 
lenses  for  the  large  peripheral  and  ignore  the  smaller, 
more  important  central  portion  of  the  pupil,  thus  choos- 
ing too  weak  convex  or  too  strong  concave  lenses  in 
positive  aberration  or  the  opposite  in  negative  aberra- 
tion. In  determining  how  much  to  allow  for  the 
cycloplegic  in  the  final  correction,  or  whether  to  give 
the  full  correction  or  not,  the  writer  always  considers 
the  degree  and  nature  of  the  aberration  present. 


CONICAL    CORNEA.  75 

Negative  Aberration. — This  is  a  condition  in  which 
rays  of  light  passing  through  the  periphery  of  each  me- 
ridian of  a  spherical  refractive  medium  focus  farther 
from  it  than  those  passing  through  its  center.  This  is 
due  to  the  fact  that  the  peripheral  has  less  refractive 
strength  than  the  central  portion.  This  condition  is 
exactly  the  reverse  of  positive  aberration.  When  the 
examiner  is  within,  between,  or  beyond  the  anterior 
focal  points,  exactly  the  reverse  will  be  observed  from 
that  which  was  noted  in  positive  aberration  (Fig.  23). 


FIG.  23. — Negative  aberration.  The  central  rays  of  light  focus  at  B, 
the  peripheral  at  A.  If  the  examiner  be  located  at  B,  the  central  area  will 
be  filled  with  light  and  the  peripheral  area  will  be  occupied  by  a  band  of 
light  moving  with  the  light  on  the  face  (plane  mirror).  If  at  A,  the  periph- 
eral area  will  be  occupied  by  a  bright  band  of  light,  the  central  by  a  dim- 
mer area  of  light  moving  against  the  light  on  the  face  (plane  mirror).  If 
midway  between  A  and  B,  the  peripheral  area  of  light  will  move  with  the 
light  on  the  face  at  the  same  rate  that  the  central  will  move  against  the  light 
on  the  face.  If  beyond  A,  both  areas  will  move  against  the  light  on  the  face, 
but  at  a  different  rate,  the  peripheral  moving  faster  and  being  brighter.  If 
within  B,  both  will  move  with  the  light  on  the  face,  the  central  being  brighter 
and  moving  faster. 


Conical  Cornea. — With  a  conical  cornea  there  is  a 
marked  negative  aberration  in  which  the  degree  of 
myopia  in  the  center  of  the  pupil  is  high,  while  that  of 
the  periphery  is  very  much  lower;  or,  perchance,  this 
portion  may  even  be  hypermetropic.  The  focusing 
point  of  the  peripheral  rays  is  much  farther  removed 
from  the  eye  than  that  of  the  central.  If  the  peripheral 
rays  focus  near  the  examiner's  eye,  a  large,  brilliant, 
rapidly  moving  light  will  be  seen  in  the  periphery 
which,  toward  the  center,  becomes  smaller,  less  bril- 


76  PHOTOSCOPY. 

Hant,  and  moves  more  slowly.  This  triangular  shaped 
area  of  light,  which  is  brilliant  at  its  base  and  dim  at  its 
apex,  moves  rapidly  around  the  center  of  the  cornea  as 
on  a  pivot.  It  must  be  remembered,  however,  that  the 
apex  of  the  cone  is  not  always  central,  and  that  under 
such  conditions  astigmatism  is  nearly  always  present. 
The  observer  should  try  to  determine  the  proper  lens 
or  lenses  for  only  the  central  area,  and  avoid  the  pe- 
ripheral ones  as  much  as  possible.  In  addition,  a  care- 
ful subjective  examination  should  be  made  in  these 
cases  after  the  pupil  has  regained  its  normal  size  (Fron- 
tispiece 7  and  8). 

Conical  Astigmatism. — R.  D.  Batten  (Ophthalmic 
Review,  January,  1897)  called  attention  to  the  phe- 
nomenon that  a  bar  of  light  while  moving;  across  the 
pupil  sometimes  changes  its  direction  or  axis  as  if  swing- 
ing around  the  apex  of  a  cone  beyond  the  margin  of  the 
cornea.  The  direction  of  the  bar  should  be  noticed 
when  it  is  at  the  center  of  the  pupil. 

Scissors  Appearance. — If  one-half,  or  more,  of  the 
refractive  media  in  the  pupillary  area  is  stronger,  or 
weaker,  than  the  remaining  portion,  it  will  be  readily 
understood  that  the  rays  passing  through  one  portion, 
or  half  of  the  pupil,  will  be  more  or  less  convergent  or 
divergent  than  those  passing  through  the  other  sections. 
One-half,  or  more,  of  each  meridian  is  stronger,  or 
weaker,  than  the  opposite  portion  of  the  same  meridian. 
If  myopia  is  present  in  both  portions,  or  is  produced  by 
the  aid  of  lenses,  the  anterior  focal  point  for  each  half 
or  portion  will  be  at  a  different  distance  in  front  of  the 
eye. 

When  beyond  both,  but  near  the  farther  anterior 
focal  point,  the  central  light  in  each  half  will  move  at  a 


SCISSORS    APPEARANCE.  77 

different  rate  in  a  similar  direction  against  the  light  on 
the  face.  This  is  also  true  if  within  both  anterior  focal 
points,  but  now  they  move  with  the  light  on  the  face. 
If  between  the  two,  the  movement  for  each  half  will 
be  opposite.  Generally  there  is  considerable  regular 


FIG.  24. — Scissors  movement.  The  refractive  power  of  the  upper  part 
of  the  dioptric  media  is  stronger  than  that  of  the  lower,  because  of  the  differ- 
ence in  curvature  of  the  upper  and  lower  part  of  the  cornea  and  lens.  The 
rays  passing  through  the  upper  part  focus  at  A,  and  cross  at  this  point. 
Those  passing  through  the  lower  part  focus  at  B.  If  the  examiner's  eye 
be  located  between  A  and  B,  he  would  see  an  area  in  the  upper  part  moving 
against,  and  one  in  the  lower  part  of  the  pupil  moving  with  the  light  on  the 
face  (with  the  plane  mirror).  The  two  areas  move  in  opposite  directions. 


astigmatism  associated  with  this  condition;  if  so,  two 
bars  of  light  will  be  seen  moving  toward  or  away  from 
each  other,  like  the  blades  of  a  pair  of  scissors,  pro- 
vided the  examiner  is  between  the  two  focal  points.  If 


B. 


FIG.  25. — Scissors  movement.  This  represents  a  case  where  the  rays 
passing  through  the  upper  part  of  the  lens  focus  before  those  passing  through 
the  lower  part,  because  of  the  inclination  of  the  lens.  (See  explanation  of 
Fig.  24.) 


one  of  these  bars  lies  in  the  visual  zone,  that  portion 
should  be  corrected  and  the  other  ignored.  If,  however, 
the  visual  zone  lies  between  the  two  bars,  a  correction 
should  be  sought  in  which  the  size,  shape,  brilliancy,  and 


78  PHOTOSCOPY. 

rate  of  movement  of  the  two  are  the  same,  while  the 
direction  of  their  movement  is  opposite.  The  difference 
between  the  two  portions  is  thus  equalized,  and  the 
result  is  the  correction  for  the  intermediate  visual  zone. 

The  scissors  appearance  is  no  doubt  generally  due  to 
the  tilting  of  the  lens  or  obliquity  of  one  or  more 
of  the  dioptric  surfaces.  It  can  be  produced  in  an  or- 
dinary lens  by  holding  it  obliquely,  or  looking  into  an 
eye  from  a  direction  at  a  considerable  angle  to  the  optic 
axis.  It  has  been  suggested  by  Dr.  James  Thorington 
that  reading  in  the  recumbent  position  might  possibly 
produce  it.  No  doubt  it  is  sometimes  congenital.  It 
is  not  infrequent  after  an  operation  on  the  cornea. 

Accommodation. — If  paralysis  or  spasm  of  ac- 
commodation or  imperfect  cycloplegia  after  the  use  of 
cycloplegics  is  suspected,  the  amount  of  accommodative 
power,  if  any  be  present,  may  be  readily  determined. 
It  is  only  necessary  to  find  the  correcting  lens  for  the 
eye  when  looking,  first,  at  some  distant  object;  second, 
at  an  object  held  close  before  the  eye  when  the  eyes 
should  strongly  converge.  The  difference,  if  any,  be- 
tween the  refractive  strengths  of  the  two  lenses  gives  the 
result.  It  may  also  be  determined  by  subtracting  the 
strength  of  the  correcting  lens  for  distance  from  the 
strength  of  the  lens  for  near,  found  by  the  surgeon  in 
dioptric  focal  lengths  by  approaching  the  observed  eye 
until  located  at  its  anterior  focal  point  for  near. 

Summary. — While  working  at  a  distance  of  one 
meter  from  the  patient  with  a  plane  mirror,  the  follow- 
ing facts  will  hold  true: 

I.  In  hypermetropia  the  central  light  will  move  with 
the  light  on  the  face;  all  meridians  will  be  alike.  A 
convex  (  +)  spherical  lens  is  needed  for  the  correction. 


SUMMARY.  79 

2.  In  emmetropia  the  same  is  found  as  in  hyper- 
metropia. 

3.  In  myopia  of  less  than  one  diopter,  again  the  same 
is  true  as  in  hypermetropia. 

4.  In  myopia  of  more  than  one  diopter,  the  central 
light  will  move  against  the  light  on  the  face,  and  the 
same  in  all  meridians;   a  concave  ( — )  spherical  lens  is 
needed  for  this  correction. 

5.  In  regular  astigmatism  the  two  chief  meridians 
which  are  at  right  angles  to  each  other  are  not  of  the 
same  strength.     Each  of  these  two  chief  meridians  is 
corrected  separately  in  the  same  manner  as  is  done  in 
cases  of  simple  hypermetropia,  emmetropia,  or  myopia. 

6.  In  irregular  astigmatism    different    parts    of  the 
same  meridian,  bearing  a  definite  relationship  to  one 
another,    have    different    refractive    strengths.       The 
irregularity   should   be   avoided   as   much   as  possible, 
and  the  same  method  used  as  in  the  conditions  men- 
tioned above. 

7.  In  positive  aberration  the  peripheral  part  of  each 
individual  meridian  has  the  same  refractive  strength  as 
the  diametrically  opposite  part,  but  is  stronger  than  the 
central  portion  of  this  same  meridian. 

8.  In  negative  aberration  the  peripheral  part  of  each 
individual  meridian  has  the  same  refractive  strength  as 
the  diametrically  opposite  part,  but  is  weaker  than  the 
central  portion  of  this  same  meridian. 

9.  In  conical  cornea  a  condition  of  exaggerated  nega- 
tive aberration  is  found.     The  rays  that  pass  through 
the  apex  of  the  cone  focus  before  those  passing  through 
the  periphery. 

10.  In  scissors  appearance  two  bars  of  light  in  the 


8O  PHOTOSCOPY. 

pupil  approach  and  recede  from  one  another  like  the 
blades  of  a  pair  of  scissors,  because  of  the  fact  that  the 
rays  of  light  through  one-half  or  part  of  the  pupil  focus 
sooner  than  those  passing  through  the  opposite  half  or 
part. 


CHAPTER  IV. 

GENERAL  CONSIDERATIONS.—  CYCLOPLEGICS.—  CON- 
CAVE MIRROR.— AIDS  TO  ACCURACY.— AUTO- 
PHOTOSCOPY.  —  RELATIVE  ADVANTAGES  OF 
PLANE  AND  CONCAVE  MIRRORS. 

General  Considerations. — The  best  method  of  keep- 
ing a  record  of  a  photoscopic  examination  is  what  may  be 
termed  "putting  it  on  the  cross."  When  the  location 
of  the  anterior  focal  point  of  the  meridian  in  which  the 
light  is  moved  has  been  found  and  the  strength  and 
denomination  of  the  lens  determined,  it  is  written  at  the 
end  of  a  line  which  is  drawn  on  paper  in  a  direction 
corresponding  to  the  meridian.  The  light  is  next  moved 
across  the  eye  in  the  direction  of  the  opposite  me- 
ridian, and  the  strength  and  sign  of  the  lens  required  for 
this  is  written  at  the  end  of  a  line  drawn  at  right  angles 
to  the  other  line, — e.  g.,  after  the  anterior  focal  point 
in  the  vertical  meridian,  axis  90,  is  found,  by  moving 
the  light  up  and  down,  a  record  is  made  by  drawing  a 
vertical  line  (a  b,  Fig.  26)  and  writing  the  strength  and 
sign  of  the  spherical  lens  which,  in  this  example,  is  as- 
sumed to  be  a  +2.OO  s.,  at  the  end  of  the  line. 

A  record  of  the  strength  of  the  horizontal  meridian, 
found  by  moving  the  light  from  side  to  side,  should  be 
made  in  the  same  manner  at  the  end  of  a  horizontal  line 
(c  </),  and  the  strength  of  the  lens  required  may  be  as- 
sumed to  be  a  +2.00  s.  also. 

In  the  various  forms  of  astigmatism  one  of  the  two 

10  81 


82  PHOTOSCOPY. 

chief  meridians  must  first  be  determined,  as  it  may  lie 
in  any  direction, — /.  e.,  at  any  axis.  The  other  chief 
meridian  is  nearly  always  at  right  angles  to  this  one. 
The  bar  of  light  is  always  seen  in  one  of  the  principal 
meridians.  For  example,  if  in  a  given  case  one  of  the 
chief  meridians,  the  correction  of  which  is  a  +2.50  s.,  is 
found  to  lie  at  axis  45°,  a  line  (a  b,  Fig.  27)  should  be 
drawn  in  this  same  direction,  and  the  strength  and  sign 
marked  at  the  end  of  this  line.  If  the  correction  of  the 
meridian  at  right  angles  is  a  +3.00  s.,  it  should  be 
recorded  at  the  end  of  its  line  c  d,  which  is  at  right  angles 
to  the  line  a  b. 

Writing  the  prescription  equivalent  for  the  result  on 


d+Z.00 


-rf+ZOO 


b 

FIG.  26.  FIG.    27. 

the  cross  is  sometimes  a  difficult  problem  for  the  be- 
ginner, and  the  following  rule  will  therefore  be  useful: 
Put  on  a  sphere  equal  to  the  strength  of  either,  but  gener- 
ally the  weaker  meridian;  add  a  cylinder  with  its  axis 
corresponding  to  that  same  meridian  whose  strength 
(with  the  correct  sign)  is  equal  to  the  difference  between 
the  two  meridians.  It  is  essential  that  the  cylinder  be 
of  the  proper  sign,  so  that  the  combined  strength  of  the 
sphere  and  cylinder  will  be  equal  to  the  strength  of  the 
opposite  meridian.  This  gives  the  correction  for  one 
meter,  if  the  examination  has  been  made  at  that  dis- 


GENERAL    CONSIDERATIONS.  83 

tance.     By  the  addition  of  a  — i.oo  s.  to  this  (explained 
farther  on)  the  correction  for  distance  is  obtained. 

To  illustrate:  By  applying  the  above  rule  to  the  ex- 
ample given  in  Fig.  27,  if  the  strength  of  the  weaker 
meridian  is  chosen,  the  sphere  will  be  +2.50  diopters; 
the  axis  of  the  cylinder  will  correspond  with  this  me- 
ridian which  lies  at  45°.  The  strength  of  the  cylinder  is 
the  difference  between  the  strengths  of  the  two  meridians, 
which  is  +.50  diopter.  The  result  is  +2.50  s.  O  +.50 
c.  axis  45°.  The  +2.50  s.  corrects  all  meridians  ex- 
cept the  stronger,  which  requires  an  additional  +.50  c. 
with  its  axis  at  45°,  because  the  refractive  strength  of  a 
cylinder  is  always  at  right  angles  to  its  axis. 

If  in  the  same  case  (Fig.  27)  the  stronger  meridian  be 
chosen,  the  strength  of  the  sphere  will  be  +3.00  diopters, 
the  axis  of  the  cylinder  will  correspond  to  that  me- 
ridian, which  is  135°.  The  strength  of  the  cylinder  is 
the  difference  between  the  strengths  of  the  two  meridians 
which  in  this  case  is  — .50  diopter,  and  the  result  is 
+3.00  s.  O  — .50  c.  axis  135°.  Now,  the  +3.00  s.  cor- 
rects all  meridians  except  the  weaker,  which  it  over- 
corrects  by  .50  diopter,  and  the  weaker  meridian, 
axis  45°,  therefore  requires  an  additional  — .50  c.  axis 
135°,  to  neutralize  this  overcorrection. 

In  a  case  where  the  result  is  represented  by  Fig.  28, 
a  +2.00  diopter  sphere  is  chosen  as  the  proper  strength 
which  corrects  all  meridians  except  the  one  at  180°, 
which  is  seen  by  the  figure  to  require  — i.oo  diopter, 
but  as  the  sphere  has  added  +2.00  diopters  in  that 
meridian,  this  result  can  only  be  obtained  by  the 
addition  of  a  — 3.00  c.  axis  90°,  which  is  the  difference 
in  strength  between  the  two  meridians.  The  result  is 
+  2.00  s.  O  — 3.00  c.  axis  90°. 


PHOTOSCOPY. 


In  this  same  case  (Fig.  28),  if  the  — i.oo  diopter  is 
chosen  as  the  strength  of  the  sphere,  all  the  meridians 
are  corrected  except  the  one  at  90°,  which,  as  seen,  re- 
quires +  2.00  diopters;  but,  as  there  is  a  — i.oo  diopter 
lens  already  before  it  in  the  sphere  the  addition  of  a 
+3.00  c.  axis  1 80°  is  necessary  to  correct  it.  The  re- 
sult is  — i.oo  s.  O  +3.00  c.  axis  180°. 

In  Fig.  29,  if  — i.oo  diopter  is  chosen  as  the  sphere, 
it  is  the  correct  result  for  all  meridians,  except  that  a 
cylinder  of — 2.00  diopters  strength  is  needed  so  as  to 
obtain  the  required  — 3.00  diopters  in  the  horizontal 
meridian,  and  the  cylinder  must  be  placed  at  axis  90°; 
the  result  here  is  — i.oo  s.  O  — 2.00  c.  axis  90°. 


FIG.  28. 


FIG.  29. 


In  the  same  figure  (29),  if  a  — 3.00  diopter  sphere  is 
chosen  as  the  strength,  every  meridian  will  be  cor- 
rected except  the  one  at  90°,  which  is  overcorrected  by 
— 2.00  diopters,  and  will  require  a  +2.00  c.  axis  180° 
to  correct  it,  giving  a  — 3.00  s.  O  +2.00  c.  axis  180°. 

The  reader  will  have  noticed  ere  this  that  in  every  case 
two  prescriptions  whose  refractive  strengths  are  equal 
may  be  taken  off  the  cross.  EVERY  PRESCRIPTION  HAV- 
ING BOTH  A  SPHERE  AND  CYLINDER,  OR  A  CYLINDER 
ALONE,  MAY  BE  TRANSPOSED  OR  CHANGED  INTO  AN 
EQUIVALENT  SPHERE  AND  CYLINDER.  THE  CYLINDER 
IN  EITHER  PRESCRIPTION  WILL  ALWAYS  BE  OF  THE 


GENERAL    CONSIDERATIONS.  85 

SAME  STRENGTH  BUT  WITH  OPPOSITE  SIGN,  AND  AT  THE 
OPPOSITE  AXIS  TO  THAT  OF  THE  OTHER.  THE  DIF- 
FERENCE IN  STRENGTH  BETWEEN  THE  SPHERES  USED 
IS  ALWAYS  EQUAL  TO  THE  STRENGTH  OF  THE  CYLINDER. 

In  taking  a  correction  off  the  cross,  it  is  always  well  to 
think  of  the  sphere  as  having  the  same  strength  in  all 
meridians.  But  if  one  meridian  is  stronger,  or  weaker, 
than  the  one  whose  strength  is  chosen  as  the  Strength 
of  the  sphere,  a  cylinder  is  needed  with  its  axis  at  right 
angles  to  that  meridian,  and  its  strength  must  be  equal 
to  the  difference. 

In  a  case  where  all  meridians  are  alike,  a  sphere  whose 
strength  is  the  same  as  any  meridian  will  correct  all, 
and  no  cylinder  is  necessary. 

It  must  be  remembered  that  while  two  prescriptions 
are  always  possible  when  a  combination  of  a  sphere  and 
cylinder  is  needed,  it  is  nearly  always  better  to  give  one 
than  the  other.  It  is  better  to  give  a  simple  cylinder  than 
a  sphero-cylindrical  equivalent.  It  is  cheaper,  lighter, 
and  usually  better  borne  by  the  patient, — e.  £.,  give  a 
+  1.00  c.  axis  90°,  rather  than  its  equivalent  +1.00  s. 
O  —1 .00  c.  axis  1 80°.  For  the  same  reasons  it  is  usually 
more  satisfactory  to  give  the  sphere  corresponding  to 
the  meridian  of  the  lowest  amount  of  ametropia, — e.  g., 
in  Fig.  27,  +2.50  s.  O  +.50  c.  axis  45°  is  better  than 
+3.00  s.  O  — .50  c.  axis  135°. 

It  is  easy  for  the  beginner  to  transpose  any  combina- 
tion of  sphere  and  cylinder  into  its  equivalent  by  first 
putting  it  on  the  cross.  Draw  one  line  in  the  direction 
of  the  axis  of  the  cylinder  and  the  other  at  right  angles 
to  it.  The  strength  of  the  sphere,  since  it  lies  in  all 
meridians,  can  be  marked  at  the  end  of  each  cross  line. 
The  strength  of  the  cylinder  must  be  marked  at  the  end 


86  PHOTOSCOPY. 

of  the  cross  line  which  lies  opposite  to  the  direction  of 

its  axis,  since  the  strength  of  the  cylinder  is  at  right 

angles  to  its  axis.     The  total  strength  of  each  meridian 

is  now  marked  at  the  ends  of  the  cross  lines,  and  the  same 

prescription  or  its  equivalent  can  now  be  taken  off  the 

cross.     Put  +3.00 s.  O  — i.oo  c.  axis  180°  on  the  cross. 

Taking  it  off  the  cross,  two  results  are  obtained, — viz.: 

+2.oo  s.  O  +1.00  c.   axis   90°,  which   is   better  than 

+3.00  s.  O  — i.oo  c.  axis  1 80°.     (See  Fig.  30.) 

If  in  a  sphero-cylindrical  combination  the  sphere  and 

the  cylinder  have  the  same  sign,  it  is  usually  the  better 

of  the  two  possible  prescriptions.     If  the  sphere  and 

cylinder  have  opposite   signs,  the 

+3.00L+2JK 

cylinder  being  stronger  than  the 
sphere,  as  in  mixed  astigmatism, 
the  prescription  which  has  the 
weaker  sphere  is  usually  the  better. 
If,  however,  the  cylinder  is  weaker 
than  the  sphere,  the  sphero-cylin- 

FlG.   30.  1-1  i  -i        1-1 

dncal  equivalent  with  like  signs 
is  usually  much  the  better  prescription. 

Our  object  in  photoscopy  is  to  locate  the  anterior 
focal  point  of  an  eye,  or,  in  other  words,  the  place  where 
light  rays  reflected  from  the  retina  focus  or  cross.  In 
myopia  they  focus  without  the  aid  of  lenses,  but  in  all 
other  conditions  lenses  are  required  to  obtain  an 
anterior  focal  point.  By  the  use  of  lenses  the  location 
of  the  anterior  focal  point  can  be  changed. 

Having  determined  the  exact  distance  of  the  anterior 
focal  point  in  front  of  an  eye,  and  knowing  the  focal 
length  of  the  lenses,  if  any  are  used,  it  is  easy  to  calcu- 
late the  strength  of  the  lenses  which  would  change  its 
location  to  any  desired  distance  in  front  of  the  eye.  It 


GENERAL    CONSIDERATIONS.  87 

will  be  necessary  to  consider  only  the  difference  in 
focal  lengths  of  different  lenses. 

Any  eye  having  an  anterior  focal  point  is  naturally 
myopic,  or  is  made  so  by  the  aid  of  lenses.  The  dis- 
tance of  this  focal  point  from  the  eye  is  the  focal  length 
of  a  lens  which  indicates  the  amount  of  myopia  present. 
Therefore,  the  addition  of  a  minus  lens,  whose  focal 
length  is  the  same  as  the  distance  of  the  anterior  focal 
point  from  the  eye,  will  permit  the  eye  to  see  at  infinity. 
The  myopia  has  been  neutralized,  and  the  eye  has  no 
longer  a  finite  anterior  focal  point.  This  is  the  same 
principle  by  which  a  plus  lens  is  neutralized  by  com- 
bining with  it  a  minus  lens  of  the  same  strength. 

Thus,  if  the  anterior  focal  point  be  at  one  meter 
(approximately  40  inches)  in  front  of  an  eye,  the  same 
distance  at  which  a  +  i.oo  diopter  or  4O-inch  spherical 
lens  would  focus  parallel  rays  of  light,  the  eye  is  i.oo 
diopter  myopic;  by  placing  a — i.oo  s.  in  front  of  it, 
the  distant  correction  will  be  obtained.  The  follow- 
ing examples  illustrate  the  above  principles: 

1.  If  the  anterior  focal  point  is  at  a  distance  of  one 
meter  (40  inches)  with  no  lens  before  the  eye,  it  is  one 
diopter  myopic;   therefore,  the  correction  of  the  eye  for 
the  distance  will  be  a  — i.oo  spherical  lens. 

2.  If  the  anterior  focal  point  is  found  to  be  at  a  dis- 
tance of  one  meter  with  a  +  i.oo  s.  before  the  eye,  the 
correction  for  distance  is  ascertained  by  the  addition  of  a 
— i.oo  s.     But  as  this  neutralizes  the   +1.00  s.  before 
the  eye,  no  correcting  lens  is  needed,  and  the  eye  is 
emmetropic. 

3.  If  the  anterior  focal  point  is  at  a  distance  of  one 
meter  with  a   +3.00  s.  before  the  eye,  the  correction  for 
distance  is  found  as  in  the  above  two  examples  by  the 


05  PHOTOSCOPY. 

addition  of  a  — 1 .00  s.  But  as  this  only  neutralizes  + 1 .00 
diopter  of  the  total  +3.00  diopters,  the  remaining  -f-a.oos. 
is  the  correction  for  the  distance,  and  consequently 
the  eye  is  2.00  diopters  hypermetropic. 

4.  If  the  anterior  focal  point  is  at  a  distance  of  one 
meter  with  a  — 3.00  s.  before  the  eye  the  correction  for 
distance  is  again  found  by  the  addition  of  a  — i.oo  s. 
to  that  already  in  front  of  the  eye.     The  sum  of  the 
two  lenses  is  a  total  of — 4.00  diopters,  the  correction  for 
distance,  and  the  eye  is  4.00  diopters  myopic. 

5.  If  the  anterior  focal  point  is  found  at  a  distance  of 
one-half  meter  (20  inches),  which  is  the  focal  length  of 
a  +2.OO  diopter  (about  20  inches)  spherical  lens,  the  cor- 
rection for  distance  would  be  found  by  the  addition 
of  a  — 2.00  s.,  because  it  neutralizes  the  2.00  diopters  of 
myopia  present. 

6.  If  the  anterior  focal  point  is  found  at  a  distance  of 
two  meters  (80  inches),  which  is  the  focal  length  of  a 

+  .50  diopter  (about  80  inches)  lens,  the  correction  for 
distance  will  be  the  addition  of  a  — .50  diopter  lens  to 
that  already  before  the  eye,  as  it  neutralizes  the  .50 
diopter  of  myopia  present. 

In  rinding  the  correction  for  distance  the  change  is 
always  made  in  the  sphere  and  never  in  the  cylinder,— 
e.  g.,  if  the  lenses  before  an  eye  for  one  meter  were  +2.00 
s.  O  +.50  c.  axis  90°,  then  by  adding  — i.oo  s.  as  the 
allowance  for  working  distance,  the  strength  of  the 
correcting  lenses  for  the  distance  will  be  found  to  be 

+  1.00  s.  O  +.50  c.  axis  90°. 

It  is  always  best  for  the  beginner  to  find  first  the 
strength  of  sphere  and  cylinder  for  the  working  distance 
by  taking  the  result  off  the  cross,  and  afterward  add 
the  neutralizing  lens  as  the  allowance  for  working  dis- 


GENERAL    CONSIDERATIONS.  89 

tance,  in  order  to  find  the  proper  distant  lens  or  lenses. 
The  expert  will  do  both  processes  at  the  same  time, 
combining  the  two  to  find  the  proper  sphere,  then 
proceeding  with  the  first  to  find  the  cylinder,  as  the 
second  process  has  nothing  to  do  with  the  strength  of 
the  cylinder. 

To  find  the  distant  correction,  always  add  a  concave 
( — )  sphere  (as  an  allowance  for  the  working  distance) 
to  the  dark-room  correction. 

EXAMPLES. 

Dark-room, —  2.00  —    .50       o.oo  +  i.oo  +  2.00 

Allowance  for  working  distance  at  i 

meter, —  i  .00  —  i  .00  —  i  .00  —  i  .00  —  i  .00 

Distant  correction, —  3.00  —  1.50  —  i.oo       o.oo  +  i.oo 

Dark-room,   —  1.50    s.    O —    -5°  c.  ax.  90 

Allowance  for  distance, —  t.oo 


Distant  correction,    — 2.50    s.    O —    -5°  c.  ax.  90 

Dark-room, +  i.oo    s.  O  +     -5°  c.  ax.  90 

Allowance  for  distance, —  i.oo 


Distant  correction, o.oo          Q  +     .50  c.  ax.  90 

Dark-room, +  3.00    s.    O  +  i.oo  c.  ax.  30 

Allowance  for  distance, —  i.oo 


Distant  correction, +  2.00    s.   O  +  I-°°  c-  ax.  30 

Dark-room, —    .50  —  o.oo  +  i.oo  +  2.00  +  3.00 

Allowance  for  working  distance  at  ^ 

meter, —  2.00  —  2.00  —  2.00  —  2.00  —  2.00 

—  2.50  —  2.00  —  i.oo        o.oo  +  i.oo 

After  placing  the  result  in  the  trial  frame,  it  is  best  to 
test  each  eye  separately  to  ascertain  if  any  change  is 
desired  either  in  the  strength  of  the  sphere  or  cylinder, 
or  a  change  in  the  position  of  the  axis  of  the  cylinder, 
found  by  rotating  the  cylinder  in  the  trial  frame.  It 
is  advisable  to  use  the  crossed  cylinder  in  making  this 
subjective  test.  (See  Ophthalmic  Record,  February, 
1904,  for  Author's  article.) 


go  PHOTOSCOPY. 

Cycloplegics. — The  question  of  the  use  of  drops  in 
order  to  paralyze  the  accommodation  and  dilate  the 
pupil — cycloplegics  which  are  also  mydriatics — is  of 
great  importance.  Their  utility  depends  chiefly  upon 
the  fact  that,  if  properly  administered,  the  accommoda- 
tion is  temporarily  suspended,  the  eye  thus  being  in  a 
condition  of  rest  and  unable  to  change  its  refractive 
strength.  Under  their  influence  the  static,  cycloplegic 
correction  is  obtained,  and  not  the  partial  and  ever- 
changing  correction  usually  demanded  by  the  otherwise 
capricious  and  inconstant  eye.  Uniform  and  complete 
paralysis  must  be  obtained,  for,  if  certain  parts  of  the 
ciliary  muscle  remain  more  active  than  others,  temporary 
astigmatism  will  be  produced.  A  common  error  is  the 
belief  that  dilatation  of  the  pupil  is  the  prime  object 
sought.  While  it  is  true  that  a  moderate  dilatation  is 
desired,  the  complete  dilatation  produced  by  all  known 
cycloplegics  is  usually  a  source  of  annoyance,  confusing 
the  appearance  in  the  central  area  and  exposing  pe- 
ripheral areas  that  the  patient  does  not  use  when  the 
pupil  is  its  normal  size.  It  is,  however,  almost  impos- 
sible to  make  the  test  correctly  when  the  pupil  is  less 
than  4  millimeters  in  diameter. 

The  following  is  my  method  of  using  the  drops 
(cycloplegics).  Usually  in  patients  under  fifteen  years 
of  age  one  drop  of  an  aqueous  solution  of  the  sulphate 
of  atropin,  varying  in  strength  from  one-fourth  to  four 
grains  to  an  ounce,  is  dropped  in  the  outer  corner  of 
each  eye  three  times  a  day,  after  meals,  for  four  con- 
secutive days.  If  the  lids  are  immediately  closed  after 
placing  a  drop  in  the  outer  corner  of  the  eye  sac,  a  thin 
layer  of  the  liquid  is  immediately  spread  over  the  sur- 
face of  the  cornea  and  eyeball.  Gentle  pressure  by  the 


CYCLOPLEGICS.  9! 

finger  over  the  inner  ends  of  the  lids  for  a  minute  or  so 
prevents  the  solution  from  draining  into  the  nose,  which 
might  produce  toxic  symptoms. 
Atropin  is  also  used, — 

1.  In  patients  over  fifteen  years  of  age  if  of  a  highly 
neurotic  temperament. 

2.  In   those  who   complain   of  previous   failures   in 
obtaining  satisfactory  lenses. 

3.  When  homatropin  has  failed  to  give  satisfactory 
results. 

4.  In  those  where  a  thorough  rest  of  the  eyes  is  in- 
dicated because  of  a  woolly  chorioid,  flannel-red  fundus, 
shot-silk  retina,  fluffy  eye  ground,  or  slight  lenticular 
striations. 

In  patients  over  fifteen  years  of  age,  not  included  in 
the  above  category,  'one  drop  of  an  aqueous  solution  of 
homatropin  hydrobromid,  four  grains  to  the  ounce, 
is  dropped  in  the  outer  corner  of  each  eye  two  or  three 
times,  at  intervals  of  five  minutes,  the  night  before,  if 
the  examination  is  to  be  made  on  the  following  morning. 
If  the  examination  is  to  be  made  in  the  afternoon,  a  few 
drops  are  placed  in  the  eye  the  morning  of  the  same  day. 
It  is  to  be  followed  immediately  before  the  examination 
by  one  drop,  from  six  to  ten  times,  at  intervals  of  five 
minutes  between  each  drop.  During  this  treatment  the 
patient  with  closed  lids  is  seated  in  a  darkened  room. 
The  examination  does  not  take  place  until  half  an 
hour  after  the  last  instillation. 

In  patients  over  forty,  the  tension  should  be  care- 
fully determined  and  the  danger  of  glaucoma  consid- 
ered, also  the  effect  on  lactation  in  nursing  mothers. 
If  there  in  an  increase  in  the  intraocular  tension 
mydriatics  are  always  contraindicated. 


92  PHOTOSCOPY. 

In  cases  of  aphakia,  and  in  most  people  over  sixty 
years  of  age,  if  the  pupil  is  not  less  than  four  millimeters 
in  diameter,  or  is  made  so  by  the  use  of  a  few  drops  of 
a  two  per  cent,  hydrochlorid  of  cocain,  or  by  a  one 
per  cent,  each  of  cocain  and  euphthalmin  solution, 
good  results  can  be  obtained  without  the  use  of  any 
cycloplegic.  In  cases  of  myopia  and  mixed  astigma- 
tism with  a  fair-sized  pupil,  good  results  may  sometimes 
be  obtained  without  the  use  of  a  cycloplegic.  However, 
the  result  is  always  more  satisfactory  with  a  cycloplegic, 
especially  as  these  patients  are  usually  more  comfortable 
after  the  enforced  rest  of  the  eyes;  and  myopic  cases,  on 
account  of  the  proximity  of  the  near  and  far  points,  do 
not  suffer  much  annoyance  from  their  use. 

No  arbitrary  rules  can  govern  each  individual  case. 
Many  things  are  to  be  considered  in  the  selection  and 
use  of  the  proper  cycloplegics,  different  examiners 
selecting  different  drugs,  and  using  them  in  a  quite 
different  manner.  Many  prefer  to  use  the  drugs  in  the 
form  of  small  soluble  discs  which  are  placed  in  the 
lower  cul-de-sac,  as  recommended  by  Dr.  Casey  A. 
Wood.  The  writer  sometimes  uses  homatropin  even 
in  children  with  good  results. 

The  completeness  of  the  paralysis  of  accommodation 
does  not  depend  solely  on  the  age  of  the  person,  but 
also  on  the  condition  of  the  ciliary  muscle  and  general 
resisting  powers.  A  bookkeeper  at  fifty  years  of  age, 
who  is  overworking  his  eyes,  may  require  a  stronger 
cycloplegic  than  many  young  people.  Homatropin, 
used  as  above  described,  is  preferable  in  the  great 
majority  of  cases,  when  the  tension  is  not  high,  and 
other  objections  to  its  use  are  not  present. 

The  Concave    Mirror. — The  same  conditions  ob- 


THE    CONCAVE    MIRROR.  93 

tain  with  the  concave  as  with  the  plane  mirror,  with  the 
following  exceptions : 

1.  The  essential  difference  between  the  use  of  the 
plane  and  concave   mirror  is   that  with  the  latter  the 
rays  of  light  may  and  should  focus  before  reaching  the 
patient's  eye,  while  with  the  former  they  cannot.     The 
following  points  should  therefore  be  observed,  otherwise 
the  rays  will  not  focus  before  reaching  the  patient's 
eye,  and  the  test  would  then  be  the  same  as  with  the 
plane  mirror: 

(a)  The  examiner  must  be  seated  at  a  greater  dis- 
tance from  the  patient  than  the  focal  length  of  the  mirror. 

(&)  The  focal  length  of  the  mirror — eight  to  ten  inches 
— should  be  much  shorter  than  the  distance  at  which 
the  examination  is  usually  made  (forty  inches,  or  one 
meter). 

(<r)  It  is  usually  best  to  place  the  source  of  light  be- 
hind, either  above  or  to  the  side  of  the  patient's  head, 
as  it  is  possible  to  have  the  source  of  light  so  near  the 
mirror  that  the  rays  will  not  focus  before  reaching  the 
patient's  eye. 

(</)  The  distance  of  the  examiner  should  be  main- 
tained as  nearly  constant  as  possible,  for  even  slight 
changes  give  rise  to  great  differences  in  the  brilliancy 
of  the  light  entering  the  patient's  eye.  If  a  movement 
is  made  toward  the  patient,  it  is  also  toward  the  source 
of  light,  and  there  is  danger  of  getting  so  near  that  the 
light  rays  will  not  have  focused  before  reaching  the 
patient's  eye. 

2.  The  examiner's  eye  and  the  anterior  focal  point 
of  the  patient's  eye  are  made  to  coincide  by  the  use  of 
lenses,  and  preferably  not  by  the  examiner  changing 
his  position. 


94  PHOTOSCOPY. 

3.  The  source  of  light  should  be  much  larger  than 
when  using  the  plane  mirror.  If  a  light  screen,  which 
is  not  necessary  but  desirable,  is  used,  the  opening 
should  be  at  least  30  millimeters  in  diameter. 

In  tilting  or  rotating  the  concave  mirror,  the  light  will 
move  on  the  face  with  the  movement  of  the  mirror,  as 
with  the  plane  mirror.  In  addition,  the  small  light 
images  on  the  surfaces  of  the  cornea,  lens,  and  trial 
lenses,  are  also  noticed.  But  the  central  light  area  in 
the  pupil  with  which  the  examiner  is  chiefly  concerned 
moves  against  the  light  on  the  face  in  emmetropia, 
hypermetropia,  and  in  myopia  of  less  than  one  diopter; 
and  with  the  light  on  the  face  in  myopia  over  one  diopter 
if  working  at  a  distance  of  one  meter.  The  relative 
movement  of  the  light  on  the  face,  and  the  central  light 
area  in  the  pupil,  with  the  concave  mirror,  is  opposite 
to  that  (the  reverse)  with  the  plane  mirror.  When  the 
central  light  area  is  moving  against  the  light  on  the  face 
with  the  concave  mirror,  convex  ( +)  lenses  are  in- 
dicated; when  the  motion  is  with,  concave  ( — )  lenses, 
until  the  usual  signs  of  being  at  the  anterior  focal  point 
of  the  eye  are  noticed. 

It  is  usually  best,  in  determining  the  exact  correction, 
to  find  two  lenses  of  as  nearly  the  same  strength  as 
possible,  with  one  of  which  the  light  moves  with  the 
light  on  the  face,  and  with  the  other,  against.  If  these 
opposite  movements  are  at  about  the  same  rate,  a  lens 
midway  in  strength  between  the  two  used  would  cause 
the  anterior  focal  point  of  the  meridian  examined  to 
coincide  with  the  examiner's  eye. 

Aids  to  Accuracy. — In  order  that  a  satisfactory  and 
accurate  result  may  be  obtained,  not  only  the  conditions 


AIDS    TO    ACCURACY.  95 

already  noted  but  also  those  about  to  be  mentioned, 
should  be  carefully  fulfilled: 

1.  The  examination  room  should  be  dark,  with  all 
light   excluded   except   the   artificial   one   used,   which 
should  be  covered  with  a  proper  chimney  or  screen, 
in  order  that  the  portion  of  the  retina  surrounding  its 
illuminated  area  may  be  as  dark  as  possible,  thus  con- 
trasting these  two  areas  and  making  the  margin  between 
them  more  distinct.     The  room  should  be  large  and 
easily  ventilated,  so  as  to  be  more  comfortable  for  both 
patient  and  examiner  than  the  usual  small  sweat  box 
or  small  closet  arranged  in  a  corner.     The  consultation 
room  is  readily  converted  into  a  sufficiently  dark  room 
by  means  of  thick,  black  curtains,  so  arranged  before 
the  windows  on  horizontal  steel  rods  that  by  the  use  of 
cords  and  pulleys  two  or  more  windows  can  be  easily 
darkened  by  one  short  pull,  the  curtain  sliding  from 
side  to  side  instead  of  from  top  to  bottom. 

2.  The  source  of  light  should  be  as  brilliant  as  pos- 
sible, with  its  brightest  part  opposite  the  aperture  in  the 
shade,  the  size  of  which  is  governed  by  a  diaphragm. 
A  5-millimeter  opening  is  usually  the  best  when  work- 
ing near  the  anterior  focal  point  of  a  meridian.    Some 
examiners,   and  nearly  all  beginners,   prefer  a  larger 
aperture,  which    is    perhaps    better  when  working  at 
a  distance  from  the  anterior  focal  point. 

3.  The  source  of  light  should  be  supported  by  a  freely 
movable  bracket,  so  that  its  distance  from  the  plane 
mirror  may  be  easily  regulated  according  to  circum- 
stances.    When  working  near  the  anterior  focal  point 
of  a  meridian  in  determining  the  correction  for  that  me- 
ridian, it  is  best  to  have  the  light  near  the  mirror,  so  that 
the  position  of  its  image,  which  appears  to  be  behind  the 


96  PHOTOSCOPY. 

mirror,  will  more  nearly  coincide  with  the  anterior 
focal  point.  By  this  means,  it  is  as  near  the  conjugate 
focus  of  the  retina  as  possible,  thus  insuring  the  best 
focus  (smallest,  with  best-defined  edge)  of  the  lighten 
the  retina,  and  consequently  a  well-defined  anterior 
focal  point.  If  the  anterior  focal  point  of  a  meridian 
is  considerably  beyond  the  mirror,  it  is  well  to  place  the 
light  farther  away,  so  that  its  image,  which  will  now  be 
farther  behind  the  mirror,  will  be  nearer  this  conjugate 
focus  of  the  retina.  For  this  reason  the  light  will  more 
nearly  focus  on  the  retina.  If  the  examiner  is  one 
meter  (forty  inches)  distant  from  the  patient,  and  the 
source  of  light  above,  or  at  the  side  of  the  patient's  head, 
fifty  inches  from  the  mirror,  the  image  of  the  light  will 
appear  to  be  fifty  inches  behind  the  mirror,  or  ninety 
inches  from  the  eye.  Now,  if  the  light  is  placed  five 
inches  from  the  mirror,  the  image  of  the  light  will 
be  forty-five  inches  from  the  eye  or  one-half  the  dis- 
tance it  was  in  the  former  case.  The  light  entering 
the  patient's  eye  in  the  latter  case  will  be  four  times 
more  brilliant  than  in  the  former,  and  if  the  anterior 
focal  point  was  forty-five  inches  from  the  eye,  there 
would  be  a  perfect  focus  on  the  retina.  (See  pp. 
37>  38-)  The  nearer  the  light  is  to  the  mirror, 
and  the  nearer  the  mirror  to  the  eye,  the  more 
brilliant  the  light  entering  the  patient's  eye;  and  the 
more  nearly  the  position  of  the  apparent  source  of 
light  and  anterior  focal  point  of  a  meridian  coincide, 
the  better  the  focus  of  light  on  the  retina  in  that 
meridian. 

4.  The  size  of  the  opening  in  the  light  screen  may 
vary.  Experts  usually  prefer  a  small  opening  of  five 
millimeters  or  less,  beginners  a  large  opening  of  ten 


AIDS    TO    ACCURACY.  Q7 

millimeters  or  more.  Theoretically,  the  smaller  the 
opening  the  better,  so  long  as  it  is  larger  than  the  sight 
hole  in  the  mirror,  as  thereby  a  smaller  and  more  dis- 
tinct retinal  illumination  may  be  obtained. 

In  determining  the  direction  or  axis  of  one  of  the 
chief  meridians  in  regular  astigmatism,  when  near  its 
anterior  focal  point,  it  is  best  to  have  the  apparent 
source  of  light  coincide  as  nearly  as  possible  with  the 
anterior  focal  point  of  the  opposite  meridian.  If 
located  near  the  anterior  focal  point  of  the  most  myopic 
(original  or  produced)  meridian,  the  source  of  light 
should  be  moved  farther  from  the  plane  mirror,  so  that 
the  apparent  source  of  light  behind  the  mirror  may 
more  nearly  coincide  with  the  anterior  focal  point  of  the 
opposite,  least  myopic,  meridian.  In  this  way  the  ret- 
inal illumination  will  be  smallest  in  the  least  myopic 
meridian,  of  an  elliptical  shape,  with  its  long  axis  corre- 
sponding to  the  most  myopic  meridian,  thus  aiding  in 
the  production  of  a  more  clearly  defined  apparent  bar 
of  light  in  the  most  myopic  meridian.  In  the  same 
way  in  working  near  the  anterior  focal  point  of  the 
least  myopic  meridian,  the  concave  mirror  may  place 
the  apparent  source  of  light  near  the  anterior  focal 
point  of  the  most  myopic  meridian,  forming  an  elliptical 
shaped  illumination  on  the  retina  with  its  long  axis 
in  the  least  myopic  meridian,  thus  assisting  in  more 
clearly  defining  the  apparent  bar  of  light  in  the  least 
myopic  meridian.  For  example,  if  located  near  the 
anterior  focal  point  of  the  horizontal  meridian  with  a 
bar  of  light  extending  across  the  pupil  in  that  meridian 
and  moving  vertically  with  the  light  on  the  face  with 
the  plane  mirror,  the  apparent  source  of  light  may  be 
placed  nearer  the  anterior  focal  point  of  the  vertical 


Qo  PHOTOSCOPY. 

meridian  by  moving  the  source  of  light  farther  from  the 
mirror,  thus  increasing  the  distance  between  the  ap- 
parent source  of  light  and  the  observed  eye.  If  the 
apparent  source  of  light  and  the  anterior  focal  point  of 
the  vertical  meridian  are  made  to  coincide,  an  elliptical 
area  of  illumination  will  be  formed  on  the  retina  in  the 
horizontal  meridian.  Light  passing  out  of  the  eye  from 
such  an  illumination  will  more  clearly  give  rise  to  the 
appearance  of  a  bar  of  light  in  the  horizontal  meridian, 
as  there  will  be  much  diffusion  in  the  horizontal  and 
little  in  the  vertical  meridian.  When  the  surgeon  is 
located  at  one,  and  the  apparent  source  of  light  at  the 
other  anterior  focal  point  of  one  of  the  chief  meridians, 
the  bar  of  light  appearance,  apparently  seen  in  the  pupil 
when  regular  astigmatism  is  present,  is  most  distinct. 

Since  the  apparent  source  of  light  is  behind  the  plane 
mirror,  this  form  of  mirror  is  usually  best  to  determine 
the  axis  of  a  bar  of  light  when  located  near  the  anterior 
focal  point  of  the  most  myopic  meridian,  and  to  find 
the  strength  of  the  proper  lens  for  each  meridian 
by  approaching  its  anterior  focal  point  from  the  side 
nearest  the  observed  eye.  The  reverse  is  true  of  the 
concave  mirror  as  the  apparent  source  of  light  is  in 
front  of  it. 

The  distance  at  which  the  examination  is  made  is 
largely  a  matter  of  individual  choice.  One  meter  is 
the  usual  distance,  although  in  certain  cases  one-half 
meter  is  the  best.  The  half-meter  distance  is  some- 
times to  be  preferred  in  cases  of  irregular  astigmatism, 
and  where  the  study  of  small  areas  of  the  pupil  is  im- 
perative. It  is  possible  to  study  conditions  at  this  dis- 
tance, which  cannot  be  clearly  observed  at  one  meter; 
but  the  examiner  must  be  careful  to  determine  the 


AIDS    TO    ACCURACY.  99 

exact  distance  at  which  he  worked  when  arriving  at  the 
final  result.  A  mistake  of  a  few  inches  is  of  considerable 
importance  when  working  very  near  the  eye,  but  of  very 
little  importance  when  one  meter  or  more  distant. 
(Randall,  Transactions,  Section  of  Ophthalmology, 
American  Medical  Association,  1894,  p.  63.)  Like- 
wise, when  very  near  the  observed  eye,  the  distance 
between  the  mirror  and  the  source  of  light  may  give 
rise  to  a  very  imperfect  focus  of  the  light  on  the  retina 
or  diffused  retinal  illumination.  It  is  often,  advanta- 
geous to  vary  the  distance  in  each  case  during  the  pro- 
gress of  the  examination.  The  writer  has  found  the 
focal  length  of  a  +1.25  s.,  or  approximately  thirty-two 
inches,  a  good  distance  at  which  to  use  this  test.  He 
does  not  notice  as  many  confusing  areas  at  this  distance 
as  at  one-half  meter.  Of  course,  a  — 1 .25  s.  must  be  added 
to  the  dark-room  result,  in  allowing  for  the  working 
distance,  to  find  the  distant  correction. 

The  writer  has  an  assistant  aid  him  in  making  this 
test.  The  assistant  measures,  by  means  of  a  meter 
stick  graduated  in  dioptric  focal  lengths,  the  distance 
between  the  patient's  and  examiner's  eyes,  in  order  that 
it  may  be  correct,  and  places  the  required  lenses  in  the 
trial  frames  as  they  are  ordered  by  the  examiner.  When 
using  the  light  close  to  the  mirror,  the  examiner  is  en- 
abled to  move  it  closer  to  or  farther  from  him  with  one 
hand,  while  he  operates  the  mirror  with  the  other.  If 
the  examiner  does  not  possess  the  writer's  shade,  which 
he  should,  when  working  with  the  light  close  to  the  mir- 
ror, he  can  hold  a  large  concave  or  plane  mirror  in  the 
left  hand  so  as  to  shade  both  his  eyes  from  the  bright 
light.  At  the  same  time  he  can  reflect  sufficient  light 
on  the  trial  case  to  enable  his  assistant  to  distinguish 


IOO  PHOTOSCOPY. 

the  lenses.  The  mirror  with  which  he  makes  the  test 
is  held  in  the  other  hand,  and  being  well  in  front  of  the 
eye,  receives  the  brightest  part  of  the  light  past  the  edge 
of  the  other  mirror.  Since  both  the  examiner's  eyes 
are  now  in  comparative  darkness,  they  are  not  so  quick- 
ly fatigued.  Many  give  up  the  use  of  this  test  because 
of  the  discomfort  caused  by  the  bright  light,  and  others 
make  the  test  in  too  great  haste  for  the  same  reason; 
but,  if  the  above-mentioned  shade  is  used,  no  difficulty 
will  be  experienced  in  this  respect. 

In  this  connection  it  might  be  well  for  the  author  to 
state  his  results  with  this  test  in  actual  practice,  as  it  is 
only  possible  to  locate  approximately  within  narrow 
limits,  never  perfectly,  the  anterior  focal  point.  In  a 
series  often  cases  he  usually  gets  accurate  results  within 
one-eighth  of  one  diopter  in  five;  in  four  others  ap- 
proximately correct  results,  so  that  the  test  is  of  the  very 
greatest  service  in  these  cases.  In  the  remaining  case  a 
good  result  is  not  obtained,  but,  nevertheless,  it  is 
usually  of  considerable  aid.  He  has,  unfortunately, 
never  had  time,  in  actual  practice,  to  make  afterward 
a  more  thorough  test  of  a  sufficient  number  of  these 
last-mentioned  cases  to  determine  just  why  the  test 
has  failed.  No  doubt,  in  some  cases  sufficient  time  and 
care  were  not  taken. 

Auto-photoscopy. — Dr.  Edward  Jackson,  in  the  re- 
cent edition  of  his  work,  devotes  a  chapter  to  auto- 
skiascopy,  and  it  has  also  been  mentioned  by  Dr. 
Charles  A.  Oliver  in  Norris  and  Oliver's  "System  of 
Diseases  of  the  Eye."  In  this  test,  one  eye  simply 
studies  the  refraction  of  the  other  through  the  medium 
of  a  mirror.  Either  a  plane  or  concave  mirror  may  be 
employed.  The  chief  difference  from  the  ordinary 


PLANE    AND    CONCAVE    MIRRORS.  IOI 

test  lies  in  the  fact  that  the  distance  between  the  observ- 
ing and  observed  eye  is  changed  twice  as  rapidly  in  this 
case  by  any  movement  of  the  surgeon  toward  or  away 
from  the  mirror,  as  it  is  when  the  surgeon  moves 
toward  or  away  from  a  patient.  The  distance  from 
the  observed  to  the  observing  eye  is  twice  the  distance 
from  the  observing  eye  to  the  mirror. 

Relative  Advantages  of  Plane  and  Concave 
Mirrors. — When  working  near  the  anterior  focal  point 
of  the  weakest,  least  myopic  meridian,  by  using  the  con- 
cave mirror  the  apparent  source  of  light,  or  image,  is 
brought  nearer  the  anterior  focal  point  of  the  strongest, 
most  myopic  meridian.  Thus,  a  better  focus  of  the 
light  on  the  retina  in  the  most  myopic  meridian,  and 
sometimes  a  better  defined  bar  of  light,  will  be  the 
result. 

Since  the  apparent  source  of  light  is  behind  the  plane 
mirror,  it  is  better  when  working  near  the  anterior 
focal  point  of  the  strongest  meridian,  for  the  same 
reason  that  the  concave  is  better  when  working  near  the 
weakest. 

In  positive  aberration,  the  concave  mirror  places  the 
apparent  source  of  light  nearer  the  focal  distance  of  the 
large  peripheral  part  of  the  lens,  and  a  better  focus  is 
obtained  on  the  retina. 

In  negative  aberration  the  plane  mirror  places  the 
apparent  source  of  light  closer  to  the  focal  point  of  the 
periphery  of  the  lens,  and  thus  produces  a  better  focus 
on  the  retina. 

The  distance  between  the  examiner  and  patient  and 
between  the  mirror  and  the  source  of  light,  with  the 
plane  mirror,  may  be  easily  changed;  but  this  is  not 
always  so  readily  done  with  the  concave,  an  advantage 


102  PHOTOSCOPY. 

in  favor  of  the  plane  mirror.  If  the  examination  must 
be  made  in  a  partially  darkened  room  by  an  ordinary 
unshaded  source  of  light,  the  concave  mirror  is  prob- 
ably better  than  the  plane,  which  latter  is  usually  to  be 
preferred  under  proper  conditions.  The  anterior  focal 
point  when  near  the  surgeon's  eye  and  the  apparent 
source  of  light  can  be  more  nearly  approximated  by 
the  plane  mirror;  hence  it  is  to  be  preferred  in  determin- 
ing the  correcting  lens. 

The  writer  first  learned  the  use  of  the  plane  mirror 
with  the  light  close  to  the  mirror,  and  of  course  usually 
prefers  that  method,  and  thinks  it  the  better  one.  Each 
method  has  its  good  and  bad  features,  but  the  writer 
still  clings  to  the  first  used  just  as  one  usually  prefers 
to  use  his  own  ophthalmoscope  rather  than  any  other. 


CHAPTER  V. 
HISTORY.— NAME.— OTHER  INSTRUMENTS. 

History. — On  December  12,  1859,  Bowman  (The 
Royal  Ophthalmic  Hospital  Reports,  vol.  ii,  No.  9,  p. 
157)  called  attention  to  the  characteristic  appearances 
of  conical  cornea  when  the  ophthalmoscopic  mirror  is 
tilted  or  rotated.  Donders,  1864,  in  his  work  trans- 
lated for  the  new  Sydenham  Society  by  Dr.  Moore,  of 
Dublin,  quotes  Bowman  as  claiming  to  find  regular 
astigmatism  of  the  cornea  and  the  direction  of  its  chief 
meridians.  He  rotated  the  ophthalmoscopic  mirror — 
while  held  at  a  distance  of  two  feet  from  the  eye  under 
examination  —  in  different  meridians  and  observed 
what  he  called  a  linear  shadow  in  some  meridians  of 
the  pupil  which  did  not  appear  in  others. 

The  use  of  the  ophthalmoscope  for  the  detection  of 
conical  cornea  and  irregular  astigmatism  became  popu- 
lar, but  its  use  in  regular  astigmatism  was  almost  en- 
tirely neglected.  Mr.  John  Couper,  in  1872,  at  the 
Fourth  International  Ophthalmological  Congress  (see 
Trans.,  p.  109)  read  a  paper  entitled  "The  Ophthal- 
moscope as  an  Optometer  in  Astigmatism,"  and 
claimed  that  the  greater  dispersion  in  one  meridian  than 
in  the  opposite  gave  rise  to  the  linear  shadows,  and  only 
established  the  fact  that  astigmatism  is  present. 

It  was  known  soon  after  the  discovery  of  the  ophthal- 
moscope by  Helmholtz  in  1851,  that  if  an  erect  image  of 
the  fundus  was  seen  at  some  distance  from  the  eye  by 

103 


IO4  PHOTOSCOPY. 

the  direct  method,  it  indicated  hypermetropia,  and  an 
inverted  one  indicated  myopia.  Couper  further  de- 
scribed a  modification  of  the  ordinary  use  of  the  ophthal- 
moscope, already  referred  to  by  Donders, — the  reversal 
of  the  image  of  the  retinal  vessels  and  their  distortion 
so  as  to  be  unrecognizable  in  certain  meridians. 

(Every  one  seems  to  have  been  totally  unaware  of  the 
observations  of  Bowman  and  Donders  until  Parent 
called  attention  to  them  in  a  paper  written  in  1880.) 

In  the  meantime,  Cuignet  of  Lille,  one  of  Pro- 
fessor Galezowski's  assistant  editors  of  the  Recueil 
d' Ophthalmologie^  was  doing  original  work  with  this 
test,  since  he  was  not  acquainted  with  Bowman's  or 
Donders'  observations.  As  he  did  not  possess  a  good 
theoretical  knowledge  of  optics,  much  of  his  labor  and 
enthusiasm  were  misdirected.  He  thought  that  the  phe- 
nomena of  the  test  were  solely  of  corneal  origin,  since 
he  still  wrongly  believed  that  ametropia  was  due  only  to 
different  shapes  and  curves  of  the  cornea.  He  wrote 
two  papers  on  the  subject,  in  1874,  claiming  that  the 
test  gives  a  practical  method  of  measuring  the  amount 
of  myopia,  hypermetropia,  and  astigmatism,  and  for 
the  first  time  mentions  lateral  movements  of  the  mirror. 
He  further  described  the  lateral  movements,  in  1877. 
Previous  to  this  he  had  revolved  the  light  on  the  eye,  but 
had  not  moved  it  straight  across  the  eye  in  the  direction 
of  a  certain  meridian. 

Little  attention  was  given  the  test  until  Cuignet's 
pupil,  Mengin,  introduced  its  use  at  Galezowski's  clinic 
in  Paris  and  demonstrated  it  to  Drs.  Parent  andLandolt. 
In  1878  Mengin  wrote  a  paper  describing  the  test 
and  gave  entire  credit  to  Dr.  Landolt  for  explanations 
of  the  causes  of  the  observed  phenomena.  Dr.  Parent, 


HISTORY.  IO5 

well  trained  in  optics,  urged  its  advantages  and  explained 
the  test  in  a  series  of  excellent  articles  published  in  the 
Recueil  d'Ophthalmologie  in  1  880-81,  pp.  65  and  229. 
It  now  became  a  more  popular  test.  Lytton  Forbes, 
at  that  time  a  clinical  assistant  in  Moorfields  Hospital, 
in  the  Royal  London  Ophthalmic  Hospital  Reports  for 
1880  (p.  62),  gives  a  minute  account  of  the  various 
phenomena  in  the  pupil,  but  he  did  not  give  a  full  ex- 
planation of  their  optical  significance,  since  at  that 
time  he  did  not  seem  to  understand  thoroughly  the 
theory  and  practice  of  the  test. 

In  1  88  1,  A.  Stanford  Morton  gave  a  full  description  of 
the  test  in  his  work  on  the  refraction  of  the  eye.  In  1882 
the  profound  scholar,  Charnley,  fully  explained  its 
optical  principles  in  the  Royal  London  Ophthalmic 
Hospital  Reports  (x,  3,  p.  344).  In  the  same  year, 
Juler  described  it  in  the  Ophthalmic  Review  (vol.  i,  p. 


In  1882  Chibret  (Annales  d'Oculistique)  pointed 
out  for  the  first  time  the  advantages  in  using  the  plane 
mirror,  and  in  1883,  J.  B.  Story,  of  Dublin  (Ophthal- 
mic Review,  vol.  xi,  p.  228),  advocated  the  use  of  the 
plane  mirror  at  a  distance  of  four  meters  from  the 
patient. 

In  1885  Jackson  (American  Journal  of  the  Medical 
Sciences,  April,  1885)  gave  a  clear  account  of  the  use  of 
the  plane  mirror,  and  he  added  much  to  our  knowledge 
by  many  different  contributions  (see  Bibliography), 
and  especially  by  the  various  editions  of  his  excellent 
monograph  on  "  Skiascopy." 

Dr.  James  Thorington  deserves  special  mention  for 
inventing  different  appliances  that  make  the  test  more 
effective  and  practicable.  He  has  done  much  to  make 
13 


IO6  PHOTOSCOPY. 

examination  with  the  plane  mirror  popular,  and  has 
written  an  excellent  working  manual. 

Dr.  A.  R.  Baker,  of  Cleveland,  Ohio,  was  one  of  the 
first  to  describe  and  recommend  the  test  in  this  country. 

(For  a  rather  complete  record  of  the  literature  on  this 
subject,  consult  the  appended  Bibliography.) 

Name. — Bowman  did  not  propose  any  special  name 
for  this  test.  Cuignet,  who  thought  that  the  play  of  light 
and  darkness  in  the  pupil  depended  entirely  on  the 
curvature  of  the  cornea,  named  it  "  keratoscopie. "  His 
premises  were  wrong  and  consequently  his  conclusions. 
Parent  called  it  "retinoscopie"  (retinoscopy),  which 
really  means  to  observe  or  to  study  the  retina, — actually 
ophthalmoscopy.  This  is  a  misnomer,  as  the  light  may 
fall  on  the  chorioid,  sclera,  or  optic  nerve  ending.  It  is 
a  much,  but  improperly,  used  term.  Chibret  proposed 
the  name  of  "  fantoscopie  retinienne,"  which  Priestley 
Smith  translated  into  "the  shadow  test,"  because 
it  was  thought  to  be  the  movement  of  a  shadow. 
Skiascopy  has  the  same  meaning.  It  is  not  the  study  of 
a  shadow,  but  of  light,  and  these  terms  are  open  to 
criticism  on  this  score.  Hartridge  proposed  "umbras- 
copy;"  Landolt,  "koroscopie;"  Galezowski,  " dioptros- 
copie."  They  are  all  open  to  objections.  Dr.  C. 
A.  Oliver  has  suggested  "fundus  reflex  test,"  a  good 
name  but  unnecessarily  long.  "  Retinophotoscopy  " 
is  objectionable  for  the  same  reason.  Marginal  or 
border  test  has  been  suggested,  but  is  also  open  to 
objection. 

The  writer  has  ventured  the  name  "  photoscopy," 
meaning  "to  examine  or  look  at  light,"  and  thinks  it 
the  best  name  for  the  test  for  the  following  reasons : 

I.  It  is  a  light  test  in  every  particular.     There  is  a 


NAME.  ID/ 

source  of  light  from  which  light  is  reflected  into  the  eye, 
causing  an  area  of  light  on  the  retina,  and,  from  this 
light  area,  light  rays  are  again  reflected.  The  examiner 
(as  a  part  or  all  of  these  rays  of  light  enter  his  eye,  after 
undergoing  more  or  less  refraction  while  passing  out  of 
the  patient's  eye)  observes  the  size,  shape,  direction,  and 
rate  of  movement  of  this  area  of  light — the  projected 
image  of  the  retinal  illumination  apparent  in  the  pupil. 

2.  Light  is  an  oscillatory  movement  of  a  supposed 
fluid  called  ether,  and  darkness  is  the  absence  of  this 
movement.     It  is  far  easier  to  consider  a  positive  than 
a  negative  condition. 

3.  Shadow  is  the  interception  of  light  by  some  object, 
and  as  no  object  intercepts  the  light  passing  out  through 
the  pupil,  no  real  shadow  is  ever  present  (certainly  the 
mirror  is  not  employed  to  throw  shadows).     It  is  true 
that  the  greater  part  of  the  retina  is  in  comparative 
darkness,  but  only  a  small  area  of  this  dark  part  en- 
ters into  the  test  and  the  illuminated  area  only  may 
have  its  location  changed.     The  shadow  surrounding  the 
central  light  area,  or  image,  might  be  spoken  of  as  an 
image  of  a  portion  of  the  dimly  illuminated  part  of  the 
retina.     On  the  other  hand,  the  light  area  or  image  of 
the  light  illumination  on  the  retina  is  always  seen  and 
studied.     Nothing  else  can  be  seen  when  at  the  point 
of  reversal,  or  anterior  focal  point  of  the  eye.     In  some 
cases,  when  at  the  anterior  focal  point  of  the  eye,  the 
whole  pupil  is  occupied  by  an  image  of  only  a  part  of 
the   retinal   illumination.     The   pupil   is   always    filled 
with  light,  and  the  reason  certain  portions  may,  and 
often  do,  appear  dark  is  because  the  light,  passing  from 
the  bright  retinal  illumination  through  these  portions 
of  the  pupil,  does  not  enter  the  examiner's  eye.     If  the 


io8 


PHOTOSCOPY. 


examiner  moves  his  eye  to  a  different  position,  the  light 
area  will  displace  the  dark  area  in  a  corresponding 
portion  of  the  pupil. 

4.  A  short,  euphonious  word  is  needed  to  describe  the 
test,  which  can  be  easily  applied  to  its  peculiar  instru- 
ments,   use,    user,    and    subject: 
photoscope,   photoscoped,  photo- 
scopist,  and  photoscopy. 

Other  Instruments.  —  Many 
different  supports  for  lenses  have 
been  suggested,  in  order  to  save 
time  and  make  it  easy  for  the  ex- 
aminer to  place  the  desired  lenses 
promptly,  and  with  as  little  incon- 
venience as  possible,  before  the 
patient's  eyes.  Dr.  H.  V.  Wiir- 
demann's  very  convenient  hand 
photoscopic  disc  has  already  been 
described  (Fig.  7).  The  Geneva 
hand  disc  differs  from  the  Wiir- 
demann  instrument  only  in  hav- 
ing the  convex  lenses  on  one 
standard,  and  the  concave  on 
another.  An  excellent  double- 
hand  photoscopic  disc  was  de- 
signed in  1903  by  J.  E.  Jen- 
nings and  is  made  by  A.  S.  Aloe 
Co.,  of  St.  Louis  (Fig.  31).  It  consists  of  two  aluminum 
frames  with  a  one-inch  opening  down  the  middle  for 
the  nose,  one  holding  18  convex  and  the  other  18  con- 
cave lenses,  placed  so  that  the  instrument,  which  is 
held  in  position  by  the  sides,  can  be  used  with  varying 
pupillary  distances.  Many  revolving  discs  containing 


FIG.  31. — Jennings'  photo- 
scopic disc. 


OTHER    INSTRUMENTS. 


lenses  have  been  arranged  by  Doyne,  Couper,  Geneva 
Optical  Company,  Jackson,  Burnett  (Transactions 
American  Ophthalmological  Society,  1888,  p.  223), 
Haines  (Ophthalmic  Review,  1886,  p.  282),  Hardy, 
C.  H.  Grain,  and  F.  G.  Murphy.  Lambert  (Trans- 
actions American  Ophthalmological  Society,  1894, 
p.  196)  describes  an  instrument  containing  a  very 
complete  series  of  lenses  so  that  both  spheres  and 


FIG.  32. — Jennings'  disc. 

cylinders  may  be  quickly  placed  before  the  eye.  One 
of  the  best  instruments  on  the  market  is  the  Meyro- 
witz  refractometer.  Probably  the  most  complete  re- 
volving photoscopic  disc  is  that  of  Jennings  (American 
Journal  of  Ophthalmology,  November,  1896,  and  April, 
1899).  It  is  constructed  on  the  same  principles  as 
the  Morton  ophthalmoscope.  The  examiner,  by  turn- 
ing a  wheel  on  the  lower  part  of  the  instrument,  which 
rotates  the  battery  of  lenses,  can  place  any  desired 


HO  PHOTOSCOPY. 

lens    before  the  observed  eye.     The  Cross  retinoskia- 
meter  is  quite  ingenious. 

In  a  very  complete  instrument,  the  examiner  is  often 
compelled  to  run  over  a  large  number  of  lenses  before 
finding  one  of  the  desired  strength,  and  this  naturally 
takes  much  time,  defeatingthe  very  object  for  which  such 
instruments  are  made.  The  chief  objection  to  most  of 
these  instruments  is  the  too  great  distance  between  the 
lenses  and  the  eyes  of  the  patient.  To  use  a  small  series 
of  lenses  giving  an  approximate  correction  quickly,  and 
followed  by  lenses  from  the  trial  case,  in  a  properly  ad- 


FIG.  33. — Axonometer.  FIG.  34. — Axonometer. 

«  justed  trial  frame,  would  seem  to  be  the  best  method. 
These  instruments  are  a  convenience  and  not  a  strict 
necessity.  With  the  more  complex,  since  the  examiner 
is  unable  to  change  his  distance  from  the  patient,  it 
will  probably  often  be  wise  to  use  the  concave  mirror 
with  the  light  behind  the  patient's  head.  The  ordinary 
trial  frame,  properly  adjusted,  keeps  the  lenses  in  a 
constant  relative  position  to  the  patient's  head,  so  that  a 
slight  movement  of  the  head  does  not  decenter  the  lens 
appreciably,  as  it  does  with  other  supports.  When  the 
examiner  has  learned  to  estimate  approximately  the 


OTHER    INSTRUMENTS.  Ill 

amount  of  ametropia  present,  when  looking  at  the  reflex, 
he  can  make  considerable  changes  in  the  strength  of  the 
lenses  until  an  approximate  correction  is  obtained,  and 
then  use  lenses  more  nearly  of  the  same  strength.  A 
large  number  of  lenses  in  a  trial  case  is  a  great  con- 
venience,— e.  g.,  if  4.75  s.  and  5.25  s.  lenses  can  be  used 
it  is  easy  to  observe  contrasts  in  the  direction  of  move- 
ment of  the  central  light  area  and  thus  determine  when 
a  5.00  s.  is  required. 

In    a    case   with    a    high    degree   of    hypermetropia 
which    is    detected    at    the    first    glance,   a    +3.00    or 


FIG.  35. — Finch's  disc. 

+4.00  s.  is  first  placed  before  the  eye  making  an 
approximate  correction;  lenses  of  nearly  the  same 
strength  are  afterward  used  until  the  correct  one  is 
obtained.  In  such  cases  it  is  unnecessary  and  unwise 
to  put  on  a  series  of  +.50  s.,  +1.00  s.,  +1.50  s., 

+2.00  s.  lenses.  Proficiency  comes  with  practice, 
and  the  expert  usually  places  but  few  lenses  before 
the  eye. 

As  it  is  sometimes  difficult  by  looking  at  the  trial 
frame  in  the  dark  room  to  determine  the  direction  or 
axis  of  the  bar  of  light  in  astigmatic  cases,  Thorington 
(Medical  News,  March  3,  1894)  has  suggested  small 


112 


PHOTOSCOPY. 


black  metal  discs  of  the  same  size  as  the  ordinary  trial 
lens,  to  be  placed  in  the  front  opening  of  the  trial  frame. 
When  the  bar  of  light  is  most  distinct  in  a  certain 
meridian,  the  axonometer  (Figs.  33  and  34)  is  turned 

until  the  two  heavy  white 
lines  appear  to  lie  in  the 
same  direction.  Dr.  Pr.ince 
(Ophthalmic  Review,  July, 
1894)  suggested  a  some- 
what similar  disc  called  an 
"Inclinometer."  R.  B. 
Finch  suggested  one  with 
a  wire  stretched  across, 
which  may  be  made  to 
conform  to  the  direction  of 
the  bar  of  light  (Fig.  35). 

H.  Wolff  presented  an 
electric  photoscope  at  the 
Heidelberg  Ophthalmo- 
logical  Congress  in  1896. 
De  Zeng  has  also  designed 
an  excellent  instrument  of 
this  type.  In  this  instru- 
ment the  distance  between 
its  convex  lens  and  lamp 
may  be  varied  so  as  to 
give  the  effect  of  either  a 
plane  or  concave  mirror  at 
FIG.  36.— De  Zeng's  luminous  different  distances  from  the 

photoscope. 

source  of  light.  These  in- 
struments are  particularly  useful  when  working  in  a 
room  not  specially  equipped  for  this  test  (Fig.  36). 


BIBLIOGRAPHY. 


AGNEW,  C.  R. 

"The  insufficiency  of  the  ophthalmoscope  as  the  sole  test  of  errors  of 

refraction."     Tr.  Am.  Ophth.  Soc.,  N.  Y.,  1880,  iii,  112-124. 
ANTONELLI,  A. 

"  Osservazioni  di  corectopia  bilaterale:    nuovo  contributo  di  oftalmo- 

metria  clinica  ed  altre  considerazioni. "     Lavori  di  din.  ocul.  d.   r., 

Univ.  di  Napoli,  1891-3,  iii,  277-299. 

"La  forme  de  la  source  lumineuse  (carre  lumineux)  pour  la  skiascopie; 

astigmometrie  et   aberroscopie    objective   de  1'oeil. "     Rec.   d'ophth., 

Paris,  1898,  3  s.,  xx,  456-462. 

"La  sorgente  luminosa  a  forma  di  quadrato  per  la  skiascopia  (astig- 

mometria  ed  aberroscopia  obbiettiva  dell'  occhio)."     Arch,  di  otlal., 

Palermo,  1898-9,  vi,  118-124. 

"I  fenomeni  schiascopici  (ombra  falcata  lineare)  e  la  miopia  acqui- 

sita,  dovuti  a  sclerosi  senile  del  cristallino  od  a  cataratta  iniziale. " 

Rendic.  d.  Cong.  d.  Ass.  ojtal.,  Ital.,  1895,  Pavia,  1896,  xiv,  319-333. 

"Aberroscopie  objective,  au  moyen  de  la  skiascopie."     Bull,  et  mem. 

Soc.  franc,  d'opth.,  Paris,  1896,  xiv,  456—467. 
BABCOCK,  W.  D. 

"The  shadow  test:    a   test   for  the  general   practitioner."     S.  Calif. 

Pract.,  Los  Angeles,  1895,  x,  461-463. 

BAKER,  A.  R. 

"Retinoscopy."     Am.  Jour.  Ophth.,  St.  Louis,  1884-5,  i>  116-119. 
"Retinoscopy."     Tr.  Ninth  Internal.  Med.  Cong.,  Washington,  1887, 

iii,  7 74-78°  • 

"Retinoscopy."     Cleveland  Med.  Gazette,  Dec.,  1885,  91. 

BARDELLI. 

"Skiascopy."     Ann.  d'ocul.,  1895,  409-440. 
"La  skiaskopia."     Ibid.,  1895,  cxiv,  401. 

BATTEN  R.  D. 

"  Conical  astigmatism. "     Ophth.  Rev.,  Jan.,  1897. 

BEAUMONT,  W.  M. 

"The  shadow  test  in  the  diagnosis  and  estimation  of  ametropia." 
London,  1890. 

BERTELE. 

"De  1'origine  et  des  causas  des  phenomenes  que  1'  on  observe  dans  le 
precede  d'  optometrie  de  Cuignet,  dit  keratoscopie  ou  skiascopie." 
Arch,  de  med.  et  pharm.  mil.,  Paris,  1894,  xxiii,  165-172. 

BlAT. 

"De  la  keratoscopie:  essai  de  perfectionnement  et  de  synthese. "  An- 
zin,  1895. 

BIESALSKI,  K. 

"Ueber  skiagraphische  Photometric."  Wochenschrijt.  Leipzig  u. 
Berlin,  1898,  xxiv,  53-55. 

BILLOT. 

"Determination  pratique  de  la  refraction  oculaire  par  la  keratoscopie 
ou  skiascopie;  application  a  Pexamen  des  consents."  Paris,  1893. 

i4  "3 


114  PHOTOSCOPY. 

BlSSELL,  E.  J. 

"Notes  on  the  shadow  test."  Jour.  Ophth.,  Otol.,  and  Laryngol.,  N. 
Y.,  1890,  ii,  327-331. 

BlTZOS. 

"Encore  quelques  mots  sur  la  skiascopie."      Ann.  d'ocul.,  Paris   1893, 

cix,  347-308- 
BOCK,  E. 

"Ueber  Skiascopie."     Memorabilien,  Heilbr.,  1890-91,  n.  F.,  x,  257- 

263. 
BROCA. 

"Theory  of   Skiascopy   (Thdorie   de   la   skiascopie)."     Ann.   d'ocul., 

Paris,  Nov.,  1903,  313. 

BURCHARDT,  M. 

"Ueber  Bestimmung  der  Schweite  und  der  Sehscharfe  durch  Linscn, 
die  sich  itn  Brennpunktsabstande  vor  dem  Auge  befinden."     Deutsch. 
med.  Wochenschrijt,  Berlin,  1877,  in,  148,  243,   539. 
"Ueber  Skiascopie  und  die  Grenzen  ihrer  Verwendbarkeit. "    Deutsch. 
mil.-arztl.  Zeitschrijt,  Berlin,  1895,  xxiv,  431-440. 

BURNETT,  S.  M. 

"Some  incidental  phenomena  of  the  shadow  test."  Tr.  Am.  Ophlh. 
Soc.,  Hartford,  1891-3,  vi,  388-397. 

"A  disk  of  lenses  to  be  used  in  determining  refraction  by  means  of 
skiascopy."  Ibid.,  1888,  p.  223. 

"Skiascopy;   with  a  description  of  an  apparatus  for  its  ready  employ- 
ment."    Arch.  Ophthal.,  N.  Y.,  1890,  xxx,  260-263. 
"The  mathematical  point  of  reversal  in  skiascopy."     Tr.  A.M.  A., 
Oph.  Sec.,  1904. 

"The  principles  of  refraction  in  the  human  eye,  based  on  the  laws 
of  conjugate  foci"  (1904). 
"Skiascopy."     Med.  News,  Philadelphia,  1888,  liii,  281-286. 

CARPENTER,  J.  W. 

"  Keratoscopy. "     Cm.  Lancet  Clinic,  1879,  n.  s.  ii,  161-163. 

CHARNLEY,  W. 

"On  the  theory  of  the  so-called  keratoscopy  and  its  practical  applica- 
tion. "  Royal  London  Ophth.  Rep.,  x,  344. 

CHAUVEL,  J. 

"  De  la  constatation  objective  de  1'astigmatisme  par  les  images  corne- 
ennes  au  conseil  de  revision."  Arch.  de.  med.  et  pharm.  mil.,  Paris, 
1886,  vii,  357-362. 

"A  propos  de  la  Skiascopie  (ancienne  ke"ratoscopie)."  Rec.  d'ophth., 
Paris,  1888,  3  s.,  x,  449. 

CHIBRET. 

"Skiascopie;  ses  avantages;  sa  place  en  ophthalmologie. "  Arch, 
d'ophth.,  Paris,  1886,  vi,  146-154. 

"De  la  skiascopie,  son  historique,  son  application  clinique. "     Festschr. 
z.  Feier,  H.  von  Helmholtz,  Hamburg  u.  Leipzig,  1891,  45. 
"  Determin.  quantitat  de  la  myop.  par  la  ke"ratoscopie  (fantoscopie  re- 
tin.)  a  1'aide  de  un  simpl.  mirror  plan."     Ann.  d1  oculist.,  1882,  Lxxxiii, 
238. 

"Astigmisme  selon  et  centre  le  regie  resultats  compares  de  1'examen 
(Keratometrie  and  Skiascopy)  et  de  1'examen  subjectif. "  Paris,  1890. 

CHOUET. 

"De  la  skiascopie  (ancienne  keratoscopie) ;  thforie  et  application." 
Rec.  d'ophth.,  Paris,  1888,  3  s.,  x,  216,  344. 


BIBLIOGRAPHY.  115 

CLAIBORNE,  J.  H.,  JR. 

" Retinoscopy,  or  the  shadow  test."     Med.  Record,  N.  Y.,  1887,  xxxii, 

587-589. 

CUIGNET,  F. 

"Keratoscopie."     Rec.  d'ophth.,  Paris,  1877,  2  s.,  iv,  59-79. 
"Images  Keratoscopiques. "     Bull,  et  mem.  Soc.  franc,  d'ophth.,  Paris, 
1877,  v,  25-29;  also,  Rec.  d'ophth.,  Paris,  1887,  3  s.,  ix,  262-265. 
"Keratoscopie,    retinoscopie,    pupilloscopie,    dioptroscopie   et   refrac- 
tion."    Rec.  d'ophth.,  Paris,  1886,  3  s.,  viii,  705;  1887,  3  s.,  ix,  n. 
"Astig.  comp.  et  obliq.  keratoscopie."      Rec.  d'ophth.,  3  s.  (L.  pp.), 
73-75- 
CROSS,  F.  R. 

"Retinoscopy."  Tr.  Ninth  Internal.  Med.  Cong.,  Washington,  1887, 
iii,  770-774. 

DARIER,  A. 

"Presentation  d'un  skiascope. "  Bull,  et  mem.  Soc.  franc,  d'ophth., 
Paris,  1894,  xii,  295,  379. 

DESJARDINS,  E. 

"De  la  keratoscopie  comme  moyen  de  diagnostic  dans  Fastigmatisme. " 
Gaz.  med.  de  Montreal,  1888,  ii,  241-245. 

DREISCH. 

"Zur  Skiaskopie. "  Deutsche  mil.-arztl.  Zeitschrift,  Berlin,  1894,  xxiii, 
255-257- 

DUANE,  ALEXANDER. 

"The  systematic  use  of  cylinders  in  making  the  shadow  test."  Ophth. 
Record,  1903,  xii,  420-424. 

DUNN,  J. 

"Some  remarks  upon  retinoscopy  as  a  method  of  determining  the  re- 
fraction of  the  nucleus  of  the  lens."  Arch.  Ophth.,  N.  Y.,  1893,  xxii, 
329-333- 

ELLETT,  E.  C. 

"An  auxiliary  skiascope."     Ophth.  Record,  1898,  n.  s.,  vii,  554-556. 

FICK,  A.  F. 

"  Die  Bestimmung  des  Brechzustandes  eines  Auges  durch  Schattenprobe 
(Skiaskopie)."  1891,  J.  F.  Bergmann,  Wiesbaden. 

FORBES,  L. 

"On  keratoscopy. "     Land.  Ophth.  Hasp.  Rep.,  1880,  x,  62. 

FULLER,  C.  G. 

"New  apparatus  for  more  exact  retinoscopy."  Homeop.  Eye,  Ear 
and  Throat  Journal,  N.  Y.,  1899,  v,  77-80. 

GLEICHEN. 

"Neue  Theorie  der  Schattenprobe."  Zeitschr.  }.  Augenhk.,  Berlin, 
July,  1904. 

GRANDELEMENT. 

"De  la  keratoscopie  ou  skiascopie;  moyen  simple  et  a  la  portee  de  tous 
pour  determiner  rapidement  la  refraction  oculaire  et  ses  anomalies; 
myopie,  hypermetropie  et  astigmatisme. "  Lyon  Med.,  1887,  Iv,  385- 
389- 

HAINES,  H. 

"A  new  instrument  for  facilitating  retinoscopy. "  Ophth.  Review,  Lon- 
don, 1886,  v,  282-284. 


Il6  PHOTOSCOPY. 

HALLETT,  G.  DEW. 

"Value  of  retinoscopy  over  ophthalmometry. "  Homeo.  Eye,  Ear 
and  Throat  Journal,  Feb.,  1902,  p.  50. 

HASBROUCK,  S. 

"Retinoscopy;  the  shadow  test."  Journal  Ophth.,  Otol.  and  Laryn- 
gol.,  N.  Y.  1889,  i,  122-132. 

HAWLEY,  C.  W. 

4'Practical  retinoscopy."  Rejractionist,  Boston,  1895-6,  ii,  129,  145, 
i6o. 

HEDD^US. 

"Zur  Skiaskopie. "     Klin.  Monatsbl.  f.  Augenhk.,  1892,  s.  327. 

HEINE. 

"  Ueber  den  skiaskopischen  Strahlenverlauf. "     Ibid.,  1901. 
"Zu  Neustatter's  Kritik  meiner  skiaskopischen  Schemata. "     Klin.  Mo- 
natsbl. j.  Augenhk.,  1902,  s.  153. 

HESS,  C. 

"Zur  Skiaskopie."     Klin.  Monatsbl.  /.  Augenhk.,  Stuttgart,  1893,  xxxi, 

I53-I59- 

"Demonstration  eines  Skiaskopes. "  23.  Vers.  d'ophth.  Ges.  zu  Hei- 
delberg, 1893,  s.  236. 

HOOR,  K. 

"Objektive  Methoden  zur  Einstellungs-(Refraktions)  Bestimmung 
der  Augen,  mit  besonderer  Beriicksichtigung  der  Retinoskopie  und  deren 
Verwerthbarkeit  f iir  den  Militararzt. "  Wiener  med.  Wochenschr.,  1888, 
xxxviii,  678,  712,  753. 

HUBERT  AND  PROUFF. 

"Ke*ratoscopie;  nouveau  Ke"ratoscope. "  Revue  Clin.  d'ocul.,  Paris, 
1884,  iv,  110-115,  l  pl- 

JACKSON,  E. 

"Skiascopy  and  its  practical  application  to  the  study  of  refraction." 
(Text-book.)     Philadelphia,  1895;  4th  edition,  Denver,  1905. 
" The  measurement  of  refraction  by  the  shadow  test,  or  retinoscopy." 
Am.  Jour.  Med.  Sci.,  Philadelphia,  1885,  n.  s.  Ixxxix,  404-412. 
"  The  best  form  and  practical  value  of  the  shadow  test  in  the  measure- 
ment of  refraction."     /.  Am.  Med.  Assoc.,  Chicago,  1886,  vii,  262-264. 
"  Retinal  illumination  for  the  shadow  test. "     Ophth.  Review,  London, 
1890,  ix,  44-48. 

"  The  position  of  the  source  of  light  and  the  observer  in  skiascopy,  or 
the  shadow  test."     Arch.  Ophth.,  N.  Y.,  1893,  xxii,  323-328. 
"Size  of  the  mirror  for  skiascopy,  or  the  shadow  test."     Phila.  Poly- 
clinic,  1894,  iii,  114. 

"The  visual  zone  of  the  dioptric  media  and  its  study  by  skiascopy." 
/.  A.  M.  A.,  Chicago,  1894,  xxiii,  342-345. 

"The  shadow  and  certain  conditions  of  accuracy  in  skiascopy."  Ann. 
Ophth.  and  Otol.,  St.  Louis,  1896,  p.  219-225. 

"The  mirror  for  skiascopy."  Am.  J.  Ophth.,  St.  Louis,  1896,  xiii, 
101-105. 

"Skiascopy  (the  shadow  test,  retinoscopy)  and  its  practical  applica- 
tion." "Sys.  of  Dis.  of  the  Eye"  (Norris  and  Oliver),  Philadelphia, 
1897,  ii,  89-109. 

"  Auto-skiascopy."     Ophth.  Review,  London,  1897,  xvi,  227-230. 
"The  distance  between  surgeon  and  patient  for  accurate  skiascopy." 
Ophth.  Record,  Chicago,  1898,  vii,  595-599,  i  pi. 


BIBLIOGRAPHY.  1 17 

JACKSON  (Continued) 

"Skiascopy. "     Ophth.  Review.,  London,  xiv,  329. 

"Skiascopy  as  a  method  of  precision."     Tr.  A.M.  A.,  Ophth.,  1903, 

p.  108. 

JENNINGS,  J.  E. 

"A  double  hand  skiascope."     Ophth.  Record,  Chicago,  July,  1903,  p. 

322. 

"The  technique  of  retinoscopy. "     Ibid.,  254. 

"An  improved  skiascope."     Am.  J.  Ophth.,  1896,  xiii,  326-328. 

JULER,  H. 

"The  theory  and  practice  of  retinoscopy  in  the  diagnosis  of  the  errors 
of  refraction."     Ophth.  Review,  London,  1881-1882,  i,  327-332. 
"  The  application  of  retinoscopy  to  the  diagnosis  and  treatment  of  the 
errors  of  refraction."     Brit.  Med.  Journal,  London,  1882,  ii,  670-672. 

KATS,  R.  A. 

"  Oski'askopii. "     Vrach,  St.  Petersburg,  1893,  xiv,  417-420. 

" Skiaskopicheskiya nablyudeniya vishkolie."  Ibid.,  1897,  xviii,  459-462. 

"K  voprosu  ob  izsliedovanii  prelomleniya  glaza   pomoshtshyu   skias- 

copii  (examination  of  refraction  of  the  eyes  by  skiascopy). "     Ibid.,  1894, 

xv,  817-820. 
KETTLESTRINGS,  F.  W. 

"Skiascopy  in  refraction. "     din.  Review,  Chicago,  Nov.,  1903,  p.  103. 
KHODIN,  A. 

"O  retinoscopii  (skiascopii)."     Vestnik  ojtalmol.,  Kiev,  1888,  v,  309- 

329- 
KHORTSEFF,  S.  N. 

"  Sravnitelniya      opredieleniya     refraktsii     glaz     skiaskopiyei,"     etc. 

Voyenno-med.  J.,  St.  Petersburg,    1898,  cxciii;  Med.  Spec.,  pt.,  1487— 

1507- 
KNOEPFLER. 

"La  keratoscopie  de  Cuignet. "     Rev.  med.  de  I'est,  Nancy,  1893,  xxv, 

289-305,  i  pi. 

KONIGSTEIN,   L. 

"Ueber  Skiascopie. "     Mitth.  d.  Wien.  med.  Doct.  Coll.,  1891,  xvii,  129, 

137,  141,  152. 

"Ueber  Skiascopie."     Wien.  Med.  Presse,  1891,  xxxii,  p.  569. 

KOTCHOROVSKI,  L. 

"Tiienevoye  izsliedovanie  glax  ili  skiaskopiya  (shadow  examination  of 

the  eyes,  or  skiascopy). "     Voyenno-med.  J.,  St.  Petersburg,  1894,  clxxix, 

485-504. 
KREUTZ. 

"  Skiascopy  (Die  Skiaskopie). "     Wien.  Med.  Wochenschr.,  Vienna,  1903, 

Sept.  26,  p.  1822. 
LAGLEYZE,  P. 

"  Relaciones  de  la  of talmometria  con  la  skiascopia. "     Tr.  Pan-Am.  M. 

Cong.,  1893,  Washington,  1895,  part  ii,  1488. 

LAMBERT,  W.  E. 

"A  refractometer  for  facilitating  retinoscopy."     N.   Y.  Eye  and  Ear 
Infirm.  Rep.,  1894,  ii,  35—38. 

"A  refractometer  for   skiascopy."      Tr.  Am.  Oph.  Soc.,    1894-1896; 
Hartford,  1897,  vii,  196-199. 

LANDESBERG,  M. 

"The  Keratoscope. "    Phila.  Med.  Times,  1882-83,  xiii,  784. 


Il8  PHOTOSCOPY. 

LAURENTY,  K. 

"Zur  Construction  des  Skiascops  nebst  Bermerkungen  ueber  Diagnose 

und  Messungen  des  Astigmatismus. "      Wiener    Med.  Presse,   1897, 

xxxviii,  1446-1452. 

"Die  Theorie  der  Skiascopie."     Ibid.,  1898,  xxxix,  1460,  1508. 
LEAHY. 

"On  keratoscopy. "     Indian  Med.  Gazette,  Calcutta,  1884,  xix,  184. 
LEHMANN,  J.  F. 

"Phantome  und  Wandtafeln  zur  Schatten probe,  Miinchen,  1898. 
LENDEN,  E.H. 

"The  method  of  Cuignet,  or  retinoscopy. "     London,  1902,  T.  Builliere 

and  Cox. 
LEROY,  C.  J.  A. 

"De  la  keratoscopie  ou  de  la  forme  de  la  surface  corneenne  de"duite 

des  images  apparentes  re'fle'chies  par  elle."      Arch,  d'ophth.,    Paris, 

1884,  iv,  140-154. 

"  Le  ph^nomene  de  1'ombre  pupillaire;  th£orie  et  application  a  la  mesure 

des  ame"tropies  (ke"ratoscopie  de  Cuignet)."     Rev.  gin.  d'ophth.,   Paris 

1887,  vi,  289,  337. 

"De  la  ke"ratoscopie. "     Rev.  gen.  d'ophth.,  i  u.  8,  1887. 
LOISEAU. 

"Applications  a  1'examen  des  hommes  de  guerre  du  proc&le  dit:   Ke"r- 

atoscopique. "     Ann.  d'ocul.,  1882,  Ixxxviii,  456. 

LUCCIOLA,    G.    AND   MAGNANI,    C. 

"La  schiascopia. "  Cior.  med.  d.  r.  esercito,  etc.,  Roma,  1896,  xliv, 
869-917. 

MACBRIDE,  N.  L. 

"Dioptoscopy."  Jour.  Ophth.,  Otol.,  and  Laryngol.,  N.  Y.,  1895,  vii, 
193-209. 

MACZEWSKI,  T. 

"Skiaskopija;  badanie  stanu  lamalnosci  oka  (Skiascopy;  examina- 
tion of  refraction  of  the  eye)."  Kron.  lek.,  Warsaw,  1887,  viii,  130- 
138- 

MAFFRE  DE  LASTANS,  L.  A.  E. 

"  De  la  valeur  du  proce"dfe  aptometrique  de  Cuignet  dans  le  diagnostic 
des  ame'tropies  chez  les  enfants.  Observations  recueillies  a  1'Hopital 
des  enfants-assistes  de  Bordeaux."  Bordeaux,  1895. 

MAUTHNER,  L. 

"Die  Bestimmung  der  Refractionsanomalien  mit  Hilfe  des  Augenspie- 
gels. "  Wien,  1867. 

MENGIN. 

"De  la  keYatoscopie,  comme  moyen  de  diagnostic  des  differents  etats 
ametropiques  de  1'oeil. "  Rec.  d'ophth.,  Paris,  1878,  2  s,  v,  122-144. 

MITCHELL,  S. 

"A  skiascopy  disc."     Ophth.  Rec.,  1897,  vi,  55-57. 

MOCHUTKOVSKI,   O.  O. 

"  Refleksomier  (Reflectometer)."  Vrach,  St.  Petersburg,  1880,  i,  104- 
107. 

MOXOYER. 

"Optome"trie  scotoscopique,  ou  determination  de  1'ame'tropie  par 
1'observation  des  phases  de  chatoiement  et  d'obscurit£  pupillaires  dues 
aux  mouvements  de  1'image  aerienne;  explication  par  la  theorie  des 
images  de  diffusion."  Revue  gen.  d'ophth.,  Paris,  1887,  v,  529;  1888, 
vii,  289,  337,  2  pi. 


BIBLIOGRAPHY.  Jig 

MORTON,  A.  S.,  AND  BARRETT,  J.  W. 

"A  clinical  investigation  of  the  merits  of  various  methods  of  practising 
retinoscopy. "  Brit.  Med.  Jour.,  London,  1886,  i,  105-108. 

MORTON,  A.  S. 

"  Refraction  of  the  eye,  its  diagnosis  and  the  correctness  of  its  errors, 
with  a  chapter  on  keratoscopy. "  London,  1881. 

MULLER. 

"Zur  Skiaskopie. "     Klin.  Monatsbl.  f.  Augenhk.,  1892,  S.  327. 

MURPHY,  H. 

"Some  points  in  retinoscopy."     Ophth.  Record,  1898,  vii,  4-6. 

NEUSTATTER,  O. 

"Ueber  die  erleichterte  objektive  Refractionsbestimmung  mittels  der 

Skiascopie  und  deren  praktische  Ausfuhrung  mittels  eines  verbesser- 

ten  Skiascopes  unter  Verwerthung  der  gewohnlichen   Brillenkasten- 

glaser."     Miinchen.  Med.  Wochenschrift,  1899,  xlvi,  83-87. 

"Die  Schatten  beim  Skiaskopieren. "     Zeitschriftf.  Augenhk.,  Berlin, 

1899,  ii,  Erganzungsheft,  73. 

"Ein  Leiterskiaskop  mit  Verwendung  der  Brillenkastenglaser,  u.  s. 

w. "     Ophth.  Ges.,  Heidelb.,  1897,  s.  267. 

"Ueber  den  skiaskopischen  Strahlenverlauf.     Eine  Wiederlegung  der 

Heine'schen  Auffassung. "    Klin.  Monatsbl.  f.  Augenhk,  s.    143   (Po- 

lemik  gegen  die  Arbeit  siehe  Ber.  f.  1902,  s.  154). 

NORRTE,  G. 

"Om  Skiascopi,  en  let  Methode  til  Bestemmelse  af  Refraktionen  ved 
Ofthalmoskopet. "  Ugesk.  f.  laeger,  Kjobenh.,  1886,  4  R,  xiv,  545-552. 

OTTO,  F. 

"  Betrachtungen  iiber  die  Schattenprobe  und  ein  einfaches  Bri'.len- 
Teiter-Handskiascop. "  Deutsch.  mil.-drztl.  Zeitschrift,  Berlin,  1899, 
xxvii,  593-620. 

OVERWEG. 

"Objektive  Bestimmung  der  Refraktion  des  Auges  durch  die  Skias- 
copie." Ibid.,  1889,  xviii,  157—162. 

PARENT,  H. 

"Expose  theorique  de  la  skiascopie. "  Arch,  d'ophth.,  1892,  xii,  s. 
560. 

"De  la  keratoscopie;  pratique  et  theorie. "  Rec.  d'ophth.,  Paris,  1880, 
3  s.  ii,  65-87. 

"Keratoscopie."     Ibid.,  1880,  424-439. 

"Expose  theorique  du  procede  d'optometrie  ophtalmoscopique  dit  de 
Cuignet  ou  skiascopie. "  Festschr.  z.  Feier,  H.  von  Helmholtz,  Ham- 
burg u.  Leipzig,  1891,  47~53- 

"Diagnost.  et  determ.  object,  de  1'astig."  Rec.  d'ophth.,  3  s.  iii,  pp. 
229-252,  1881. 

PERKINS,  F.  M.,  AND  TAIT,  T.  W. 

"An  instrument  to  facilitate  the  retinoscopic  examination  of  ametropia. " 
Ann.  Ophth.  and  Otol.,  St.  Louis,  1896,  p.  537-541. 

PETELLA,  G. 

"Sulla  schiascopia;    norme  pratiche  e  teoriche  per  determinare  obbiet- 

tivamente  la  refrazione  statica  dell'  occhio. "     Ann.  di  med.  nav.,  Roma, 

1897,  iii,  265-319. 
PFLUEGER,  E. 

"Skiaskopie."      Cor.-Bl.  }.  schweiz.  Aerzte,  Basel,  1885,  xv,  361-366. 


I2O  PHOTOSCOPY. 

POLVAKOFF. 

"  Opredielenie  refraktsii  glaz  pryamim  os\-ieshtsheniem  d-ra  Cuig- 
net."  St.  Petersburg,  1893. 

PURVES,  W.  L. 

"A  method  of  determining  the  anomalies  of  refraction  of  the  human 

eye."     London,  1873. 
RANDALL,  B.  A. 

"Retinoscopy  as  a  crucial  test  in  measuring  errors  of  refraction." 

Jour.  A.  M.  A.,  Chicago,  1894,  xxiii,  340. 
REIK,  H.  O. 

"The  practical  use  of  skiascopy."     Maryland  Med.  Jour.,  Baltimore, 

1896-7,  xxxvi,  109. 
"REPORT  on  the  value  of  objective   tests  for  the   determination  of  ame- 

tropia  by  ophthalmoscopy,  ophthalmometry,  skiascopy;  by  the  special 

committee  of  the  section  on  ophthalmology  of  the  American  Medical 

Association."     Jour.  A.  M.  A.,  Chicago,  1894,  xxiii,  333-379. 
RITZOS,  G. 

"La  skiascopie  (ke"ratoscopie)."     Paris,  1892. 

ROBERTS,  W.  H. 

"  Retinoscopy  as  a  method  of  measuring  errors  of  refraction. "  S.  Calif. 
Pract.,  Feb.,  1901. 

ROLLAND. 

"Theory  of  skiascopy  (Theorie  de  la  skiascopie)."  Annalcs  cTocu- 
listique,  Dec.,  1905,  p.  428. 

ROTH,  A. 

"Ueber  Skiaskopie,  nebst  Demonstration  neues  skiascopischer  Instru- 
ment." Deutsch.  mil.-artzl.  Zeitschri/t,  Berlin,  1891,  xx,  532-551. 

RUPPEL. 

"Zur  Skiaskopie."  Von  Graefe's  Arch.  f.  Ophth.,  1892,  xxxviii,  2  s. 
174. 

SEGAL,  S.  M. 

"O  niekotorikh  obyektivnikh  sposobakh  opredleleniya  refraktsii  glaza 
(skiaskopia,  vasoscopia,  sposob  Schmidt-Rimpler'a  i  sposob  Fick'a) 
(On  several  objective  methods  of  determining  refraction  of  the  eyes — 
methods  of  Schmidt-Rimpler  and  Fick)."  Vestnik  oftalmol.,  Kiev, 
1895,  xii,  28-45. 

SGROSSO,  P. 

"  Communicazione  cliniche  di  ottometria,   ottalmometria  e  schiasco- 
pia. "     Atti  d.  r.  Accad.  mcd.-c.hir.  di  Neapoli,  1894,  xlviii,  43-57. 
"Guida   practica   per   la   determinazione   della.     Refrazione   oculare 
mediante  la  schiascopia. "     Napoli,  1897. 

SHIMANOYSKI,  A.  F. 

"O  skiaskopii."      Vestnik  ojtalmol.,  Kiev,  1895,  xli,  i;   121,  243,  i  pi. 

SHIRER,  J.  W. 

"A  practical  application  of  the  skiascope. "     N.  Y.  Med.  Jour.,  1899, 

Ixix,  525-528. 
SIMANSKI,  A. 

"  Skiaskopicheskiy   sposob  opredleleniya   refraktsii   glaza   (Skiascopie 

method  of  determining  refraction  of  the  eye)."     Voyenno-med.  Jour., 

St.  Petersburg,  1897,  cxc;  Med.-Spce.,  pt.  447-459. 
SMITH,  P. 

"  A  simple  ophthalmoscope  for  the  shadow  test. "     Ophth.  Rev.,  London, 

1884. 


BIBLIOGRAPHY.  121 

SNELLEN,  H.,  Jr. 

"  Skiaskopie. "  Versl.  Nederl.  Gasth.v.Ooglijders,  Utrecht,  1887,  No. 
JI>  3J-34- 

"Skiaskopi."  Nederl.  Tijdschr.  v.  Geneesk.,  Amsterdam,  1889,  2 
R,  xxv,  153. 

STEVENSON,  M.  D. 

"  A  shade  to  protect  the  examiner's  eyes  from  the  bright  light  when  work- 
ing with  the  source  of  light  close  to  the  mirror  in  photoscopy  (retinos- 
copy)."  Ophth.  Record,  Feb.,  1904. 

STORY,  J.  B. 

"The  estimation  of  refraction  by  retinoscopy  before  and    after   atro- 
pinization. "     Ophth.  Re-view,  London,  1883,  ii,  294-300. 
"The  advantages  of  the  plane  ophth.  mirror  in  retinoscopy."     Ibid., 
ii,  p.  228. 

STRATJB. 

"De  praktische  toepassing  der  schaduwproef  van  Cuignet. "  Ned- 
erl. Tijdschr.  v.  Geneesk.,  Amsterdam,  1891,  2  R,  xxxvii,  d.  i.,  509. 

SUREAU,  H. 

"  Skiascope-Optometre. "     Bull,    et  mem  Soc.   franc,   d' ophth.,    Paris, 

1894,  xii,  379-389. 

"Skiascopie  et  skiascope  optometre. "     Ibid.,  1894. 

THOMPSON,  J.  H. 

"Retinoscopy  in  extreme  degrees  of  ametropia. "  Am.  Jour.  Ophth., 
St.  Louis,  1886,  iii,  338-342. 

THOMSON,  H.  W. 

"Convenient  instrument  for  rapid  retinoscopy."  Ophth.  Review, 
London. 

THORINGTON,  J. 

"A  skiascopic  eye."     Jour.  A.  M.  A.,  1895,  xxiv,  13. 
"A  modified  skiascope."     Philadelphia  Polyclinic,  1893,  ii,  329. 
"Lenses  for  the  study  of  the  scissors  movement,  conic  cornea,  and 
spheric  aberration  with  the  retinoscope. "     Jour.  A.  M.  A.,  1897,  xxix, 
1261. 

"Retinoscopy  (or  Shadow  Test)  in  the  determination  of  refraction  at 
one  meter  distance  with  the  plane  mirror."  (Text-book)  Philadelphia, 
1897;  3d  edition,  1899. 

"Some  remarks  on  skiascopy,  or  the  shadow  test."  Ann.  Ophth. 
and  Otol.,  St.  Louis,  1895,  iv,  5-10. 

"De  Zeng  luminous  retinoscope."  College  of  Physicians  of  Phila- 
delphia, Section  on  Ophthalmology,  Ophth.  Record,  p.  349.  1902. 

TIEMINSKI. 

"  The  determination  of  the  degree  of  ametropia  by  retinoscopy. "  Bull, 
et  Weiner  Soc.  Franc,  d' ophth.,  1887;  Bulletin  0}  Memoirs,  Paris,  1887. 

TRUKART-FELLIN,  H. 

"Ueber  Skiaskopie."  St.  Petersburg  med.  Wochenschrijt,  1893,  n.  F., 
x,  65-70;  3  diag. 

URIBE  TRONCOSO,  M. 

"Quelques  observations  sur  la  pratique  de  la  coreskiascopie. "  M  em. 
Soc.  dent.,  "Antonio  Alzate,"  Mexico,  1897-8,  xi,  5-9. 

VALK,  F. 

"The  subjective  method  for  the  determination  of  the  refraction.' 
Ophth.  Record,  Chicago,  1898,  vii,  621-626. 

15 


122  PHOTOSCOPY. 

VELYAMOVICH. 

"Ob  uproshtshenii  sposoba  skiaskopicheskavo  opredleleniya  stepeni 

anomaliy  refraktsii  (On  the  simplification  of  the  skiascopic  method  of 

determining  the  degree  of  anomalies  of  refraction)."     Voyenno-med. 

Jour.,  St.  Petersburg,  1898,  cxcii,  Mcd.-Spcc.,  pt.,  1098-1102. 
VESZELY. 

"  Ueber  Skiaskopie. "     Wiener  klin.  Wochenschrift,  1889,  ii,  999-1004. 
WECKER,  L.  DE,  AND  MASSELON,  J. 

"La  keratoscopie  clinique."     Ann.  d'ocul.,  Bruxelles,  1883;  xc,  165- 

176. 
WEEKS,  J.  E. 

"  Retinoscope,  pupillometer,  and  strabisometer  combined. "     Med.  Rec., 

N.  Y.,  1889,  xxxvi,  167. 
WEILAND,  C. 

"What  is  the  cause  of  the  shadow  in  skiascopy?     A  criticism  on  the 

current  theory."     Med.  News,  Philadelphia,   1895,  Ixvii,  399-402. 

"A  new  eye  model  (anaklasimeter)  for  determining  the  refraction  by 

ophthalmoscopy  and  retinoscopy. "     Ibid.,  1893,  Ixiii,  41. 

WIESNER,  D.  H. 

"Retinoscopy."     N.  Y.  Med.  Jour.,  March  28,  1903,  p.  548. 

WOLFF. 

"Ein  neues  Scheibenskiascop  mit  selbstthatigem  Spiegelapparat. " 
Klin.  Monatsbl.  /.  Augenheilk,  1893,  xxxi,  439-447. 
"Ueber  die  Skiaskopietheorie,  skiaskopische  Refraktionsbestimmung 
und  iiber  mein  elektrisches  Skiaskopophthalmometer,  nebst  Bemer- 
kungen  iiber  die  Spharische  aberration  und  die  Akkommodationslinie 
des  Auges. "  Bericht  iiber  die  30.  Versammlung  d.  Ophth.  Gesellsch., 
Heidelberg,  s.  150,  1902. 

"Ueber  das  elektrische   Skiaskop."     Ibid.,  1900. 
"Ueber  die  Skiaskopietheorie  und  iiber  mein  elektrisches  Skiaskop- 
ophthalmometer."    Zeitschr.   ).    Augenheilk.,    1902,    s.   213.     Berlin: 
Karger. 

"The  skiascopy  theory  (Ueber  die  skiaskopie-Theorie)."    Ibid.,  Berlin, 
September,  1900,  p.  490. 

WURDEMANN,    H.    V. 

"A  simple  skiascope."     Am.  J.  Ophth.,  1891,  viii,  223. 
"Skiascopy   (the  shadow  test)  in  the  determination  of  the  ocular  re- 
fraction."    International  Clinics,  vol.  i,  6th  Series. 
"  The  use  of  skiascopy  (the  shadow  test)  in  the  determination  of  re- 
fractive errors."     Am.  Jour.  Ophth.,  St.  Louis,  1890,  vii,  137-147. 
"The  status  of  skiascopy."     Jour.  A.  M.  A.,  Chicago,   1894,    xxiii, 

341- 

"  The  relation  of  the  objective  to  the  subjective  methods  for  ascertaining 
the  ocular  refraction."     Ophth.  Record,  Chicago,   1897,  vi,  569-578. 
ZIMMERMAN,  W.  M. 

"An  adjustable  lamp  and  light-screen  for  the  shadowiest."     Annals 
0}  Ophthal.  and  Otol.,  1896. 


INDEX 


ABERRATION,  negative,  75,  79,   101 

positive,  73,  74,  79,  101 
Accommodation,   19,  20,  53,  78 
Accuracy,  18 

aids  to,  94,  95,  96,  97,  98,  99,  100 
Albinos,  55 
Amblyopia,   19 

Anterior  focal  point,  17,  30,  31,  46, 
57,58,61,62,63,64,65,73, 
74,  76,  86,  87,  88,  96,  102 
distinctness  of,  38 
Aphakia,  19,  92 
Argand  burner,  23 
Astigmatism,  18 
conical,   76 
crossed,  72 

irregular,   70,  71,  72,   79 
of  the  cornea,  71 
of  the  lens,  70,  71 
mixed,  40 
regular,  30,  64,  65,  66,  67,  68,  69, 

7°.  ?i,  79.  97 
Atropin,  90,  91 
Auto-photoscopy,   100,   101 
Axonometer,   112 


BAKER,  106 

Band  appearance,   73 

Bar  of  light,  65,  66,  67,  68,  69 

apparent  movement  of,  69,   70 
when  most  distinct,  98 

Batten,   76 

Beginner,  suggestions  for,  19,  20,  21 

Bibliography,    113,    114,    115,    116, 
117,  118,  119,   120,   121,  122 

Blondes    55 


Bowman,   103,  104,   106 
Bracket,   an   adjustable,  23,  24,  95 
Brightness  of  light,  37,  38,  45,  46,  96 
Brunettes,  55 
Burnett,  27,   109 


CATARACT,  70,  71 
Catoptric  images,  56 
Central  image,   18 

movement  of,  57,  59,  60,  6 1 

resemblance  to  source,  18 
Charnley,  105 
Chibret,  105,  106 
Cocain,  92 
Concave  mirror,   17,  38,  98 

advantages  of,   101,  102 

use  of,  92,  93,  94 
Conical  cornea,  75,  76,  79 
Conjugate  focus,  31 
Couper,   103,   104,   109 
Cover  chimney,  24,  25 
Grain,  109 
Cross,  no 
Cuignet,  104,  106 
Cylinder,  crossed,  89 
Cycloplegics,  72,  90,  91,  92 
methods  of  using,  90,  91 


DEFINITION,  17 
DeZeng,   112 

Diagrams,  explanation  of,  42,  43 
Difficulties,  56,  72,  73,  74 
Diffusion  circle,  30,  50 
Dioptric  focal  lengths,  26,  27,  54,  65, 
99 


123 


INDEX 


Dioptroscopie,   106 
Discs,   108,   109,  no 
Distance,  37,  98,  99,  101,  102 

working,  allowance  for,  87,  88,  89 
Donders,   103,  104 
Doyne,  109 


ELECTRIC  light,  23 
Emmetropia,  29,  57,  58,  59,  60,  79 
Erect  image  (Explanation  in  Illus- 
trations), 35,  36,  58,  59,  61,  62 
Euphthalmin,  92 
Examination,  subjective,  76 
Experiments,  48,  49,  50 

FANTOSCOPIE  retinienne,  106 
Far-point,  31 
Finch,  112 
Forbes,  105 
Fundus-reflex  test,  106 


GALEZOWSKI,  106 
General  considerations,  81 
Geneva,  108,  109 
Glaucoma,  91 


HAINES,  109 

Hardy,  109 

Hartridge,  106 

Helmholtz,  103 

History,  103,  104,  105,  106 

Homatropin,  91,  92 

How  to  use  the  mirror,  21 

Hyaloid  artery,  56 

Hypermetropia,  18,  30,  60,61,62,  78 

Hypometropia,  62,  63,  64 

ILLITERATES,  19 
Inclinometer,  112 
Intraocular  tension,  91 
Inverted  image  (Explanation  in  Il- 
lustrations), 39,  40,  63,  64 


JACKSON,  105,  109 
Jennings,  108,  109 
Juler,  105 


KERATOSCOPIE,  106 
King,  26 


LAMBERT,  109 
Landolt,  104,  106 
Lens,  opacities  of,  70,  71 
Lenses,  32,  43,  53 

neutralizing,  59,  87,  88 

reflections  from,  56 
Light,   apparent  source  of,   35,  36, 

37,  38,  98 
desirable  distance  of,  38,  39, 

40 
area,  17 

at  observer's  face,  41,  46,  47,60 
direction  of,  32,  33,  34,  44,  45 
•entering  examiner's  eye,  44,  45, 

not  entering  examiner's  eye,  44, 

45 

screen,  24,  25,  52 
source  of,  23,  95 
opening  in,  94,  95,  96,  97 

MACULA,  53,  69 

Marginal  or  border  test,   106 

Mengin,  104 

Meridians,  chief,  66,  82,  97 

Meter  stick,  26,  27,  54 

Meyrowitz,  109 

Mirror,  21,  22,  23 

perforation  of,  21 

reflection  from,  35,  37,  38,  39, 

54 

sight  hole  in,  21,  22 
silvering  of,  21 
size  of,  22,  23 
tilting  of,  35,  36,  37,  54,  55 
Moore,  103 


INDEX 


125 


Morton,  105,  109 

Movement  of  light,  degree  and  rate 

of,  46,  47 
direction  of,  with  plane  mirror, 

57 

with  concave  mirror,  94 
Mulattoes,  55 
Murphy,  109 
Mydriatics,  90 

Myopia,  18,  29,  31,  62,  63,  64,  79,  87 
artificial,  31 


NAME,  106 

reasons  for,  106,  107,  108 
Near  point,  31 
Nodal  points,  47 
Nystagmus,  19 


OBSERVATIONS,  48,  49,  50 
Observer,     beyond    anterior    focal 
point,  44,  45 

movement  of,  59,  61,  63,  64 

vision  of,  20,  52 

within  anterior  focal  point,  43,  44 
Oliver,   106 
Operative  measures,   19 


PARENT,  104,  106 

Patient,    where   and   how   to   look, 

53.  54 
Photoscope,  21,   108 

varieties  of,  21 
Photoscoped,  108 
Photoscopist,  1 08 
Photoscopy,  17,  106,  108 

principles  of,  34,  35,  36,  37,  38, 

39,  40,  41,  42,  43,  44,  45 
value  of,  1 8 

Plane  mirror,  17,  35,  37,  40 
advantages  of,  101,  102 
common  method  of  use,  52,  53, 

54,  55 
practical  use  of,  51 


Plane  mirror,  when  most  useful,  98 

why  used  first,  51,  52 
Point  of  reversal,  31 

mathematical,  47 

practical,  47 

to  find,  43,  47,  58,  59,  61,  62,  63 
Position  of  light,  52 
of  mirror,  52 
of  observer,  52 
of  patient,  52 
Prescription  writing,  82 

illustrations  of,  83,  84,  85,  86 

rule  for,  82 

transposing,  84,  85,  86 
Principles,   underlying,   28,   29,   30, 

3i>  32,  33.  34 
Prince,  112 
Pupil,  size  of,  90,  92 

compared  to  window,  33,  34 
Pupillary  area,  19,  55,  56,  57 
dark,  42 
light,  42 

what  to  avoid  in  studying,  56 
shadows,  17,  42 


RECORD,  method  of  keeping,  81,  82, 

83,  84,  85 
Results,  19,  100 
Retina,  dark  portion  of,  18,  34,  42, 

69 
Retinal  illumination,  17,  18,  31,  42, 

96,  97 
compared  to  lamp  placed  in  eye, 

34,  4i 

light  passing  from,  41,  98 

position  of,  69 

shape  of,  50 
Retinophotoscopy,  106 
Retinoscopy,  106 
Room,  27,  52,  95 


SCHEMATIC  eyes,  20 

Scissors  appearance,  76,  77,  78,  79, 

80 


126 


INDEX 


Shade,  protecting,  25,  52,  99,  100 
Shadow,  107 

test,  106 

Smith,  Priestley,   106 
Source  of  light,  52 
Spherical  aberration,  50,  56 
Stevenson,  25,  26,  27,  68,  69,  89 
Story,  105 
Strabismus,  54 
Summary,  78,  79,  80 

THORINGTON,  24,  78,  105,  in 
Trial  case,  25,  26 


Trial  frame,  26,  53 


UMBRASCOPY,  106 


WELSH ACH,  23 

Wolff,  112 

Wood,  Casey  A.,  92 

Wiirdemann,  26,  27,  108 


YOUNG  children,  19 


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WITH  313  TEXT-ILLUSTRATIONS  AND  6  COLORED  PLATES 

For  this  new  edition  the  text  has  been  very  thoroughly  revised,  and  the  work 
enlarged  by  the  addition  of  new  matter  to  the  extent  of  some  one  hundred  pages. 
There  have  been  added,  amongst  other  subjects,  chapters  on  the  following  :  X-Ray 
Treatment  of  Epithelioma,  Xeroderma  Pigmentosum  ;  Purulent  Conjunctivitis  of 
Young  Girls  ;  Jequiritol  and  Jequiritol  Serum  ;  X-ray  Treatment  of  Trachoma  ; 
Infected  Marginal  Ulcer  ;  Keratitis  Punctata  Syphilitica  ;  Uveitis  and  Its  Varieties  ; 
Eye- ground  Lesions  of  Hereditary  Syphilis  ;  Macular  Atrophy  of  the  Retina; 
Worth's  Amblyoscope  ;  Stovain,  Alypin  ;  Motais'  Operation  for  Ptosis  ;  Kuhnt- 
Miiller's  Operation  for  Ectropion  ;  Haab's  Method  for  Foreign  Bodies;  and 
Sweet's  X-Ray  Method  of  Localizing  Foreign  Bodies.  Other  chapters  have  been 
rewritten.  The  excellence  of  the  illustrative  feature  has  been  maintained. 


PERSONAL  AND   PRESS  OPINIONS 


Samuel  Theobald,  M.D., 

Clinical  Professor  of  Ophthalmology,  Johns  Hopkins  University,  Baltimore. 
"  It  is  a  work  that  I  have  held  in  high  esteem,  and  is  one  of  the  two  or  three  books  upon 
the  eye  which  I  have  been  in  the  habit  of  recommending  to  my  students  in  the  Johns  Hopkins 
Medical  School." 

W.  Franklin  Coleman,  M.  D., 

Professor  of  Diseases  of  the  Eye,  Postgraduate  Medical  School,  Chicago. 
"I  am  very  much  pleased  with  deSchweinitz's  work  and  will  recommend  it  to  the  members 
of  my  class  as  a  most  reliable,  complete,  and  up  to  date  text-book." 

British  Medical  Journal 

"A  clearly  written,  comprehensive  manual.  One  which  we  can  commend  to  students  as  a 
reliable  text-book,  written  with  an  evident  knowledge  of  the  wants  of  those  entering  upon  the 
study  of  this  special  branch  of  medical  science." 


SAUNDERS'    BOOKS   ON 


GET  A  •  THE  NEW 

THE  BEST  J\  HI  C  f  1  C  Cl  II  STANDARD 

Illustrated   Dictionary 


Just  Issued— New  (4th)  Edition 


The  American  Illustrated  Medical  Dictionary.  A  new  and  com- 
plete dictionary  of  the  terms  used  in  Medicine,  Surgery,  Dentistry, 
Pharmacy,  Chemistry,  and  kindred  branches;  with  over  100  new  and 
elaborate  tables  and  many  handsome  illustrations.  By  W.  A.  NEWMAN 
DORLAND,  M.  D.,  Editor  of  "  The  American  Pocket  Medical  Diction- 
ary." Large  octavo,  nearly  840  pages,  bound  in  full  flexible  leather. 
Price,  54.50  net;  with  thumb  index,  55.00  net. 

WITH   2000    NEW  TERMS 

In  this  edition  the  book  has  been  subjected  to  a  thorough  revision.  The 
author  has  also  added  upward  of  two  thousand  important  new  terms  that  have 
appeared  in  medical  literature  during  the  past  few  months. 

Howard  A.  Kelly.  M.  D.. 

Professor  of  Gynecology,  Johns  Hopkins  University,  Baltimore. 

"  Dr.  Dorland's  Dictionary  is  admirable.     It  is  so  well  gotten  up  and  of  such  convenient 
size.     No  errors  have  been  found  in  my  use  of  it." 

Theobald's 
Prevalent  Diseases  of  the  Eye 


Prevalent  Diseases  of  the  Eye.  By  SAMUEL  THEOBALD,  M.  D., 
Clinical  Professor  of  Ophthalmology  and  Otology,  Johns  Hopkins 
University.  Octavo  of  550  pages,  with  200  text-cuts  and  several 
colored  plates 

JUST  READY— FOR  THE  PRACTITIONER 

With  few  exceptions  all  the  works  on  diseases  of  the  eye,  although  written 
ostensibly  for  the  general  practitioner,  are  in  reality  adapted  only  to  the  specialist ; 
but  Dr.  Theobald  in  his  book  has  described  very  clearly  and  in  detail  only  those 
conditions,  the  diagnosis  and  treatment  of  which  come  within  the  province  of  the 
general  practitioner.  The  therapeutic  suggestions  are  concise,  unequivocal,  and 
specific,  in  every  case  only  one  course  of  definite  treatment  being  given.  ( >ver 
200  text-illustrations  and  several  colored  plates  greatly  aid  in  presenting  the  sub- 
ject in  a  lucid  and  practical  way.  It  is  the  one  work  on  the  Eye  written  per- 
emptorily for  the  general  practitioner. 


EYE,  EAR,  NOSE,  AND    THROAT. 


American  Text-Book  of 
Eye,  Ear,  Nose,  and  Throat 


American  Text-Book  of  Diseases  of  the  Eye,  Ear,  Nose,  and 
Throat.  Edited  by  G.  E.  DE  SCHWEINITZ,  M.  D.,  Professor  of  Ophthal- 
mology in  the  University  of  Pennsylvania  ;  and  B.  ALEXANDER  RANDALL, 
M.  D.,  Clinical  Professor  of  Diseases  of  the  Ear  in  the  University  of 
Pennsylvania.  Imperial  octavo,  1251  pages,  with  766  illustrations,  59 
of  them  in  colors.  Cloth,  $7.00  net ;  Sheep  or  Half  Morocco,  $8.00  net. 

This  work  is  essentially  a  text-book  on  the  one  hand,  and,  on  the  other,  a 
volume  of  reference  to  which  the  practitioner  may  turn  and  find  a  series  of  articles 
written  by  representative  authorities  on  the  subjects  portrayed  by  them.  There- 
fore, the  practical  side  of  the  question  has  been  brought  into  prominence.  Par- 
ticular emphasis  has  been  laid  on  the  most  approved  methods  of  treatment. 

American  Journal  of  the  Medical  Sciences 

"  The  different  articles  are  complete,  forceful,  and,  if  one  may  be  permitted  to  use  the  term, 
'snappy,'  in  decided  contrast  to  some  of  the  labored  but  not  more  learned  descriptions  which 
have  appeared  in  the  larger  systems  of  ophthalmology." 

Hyde  and  Montgomery's 
Syphilis  and  Venereal 

Syphilis  and  the  Venereal  Diseases.  By  JAMES  NEVINS  HYDE, 
M.  D.,  Professor  of  Skin,  Genito-Urinary,  and  Venereal  Diseases,  and 
FRANK  H.  MONTGOMERY,  M.  D.,  Associate  Professor  of  Skin,  Genito- 
Urinary,  and  Venereal  Diseases  in  Rush  Medical  College,  in  Affiliation 
with  the  University  of  Chicago,  Chicago.  Octavo  volume  of  594  pages, 
profusely  illustrated.  Cloth,  $4.00  net. 

SECOND  EDITION,  REVISED  AND  GREATLY  ENLARGED 

In  this  edition  every  page  has  received  careful  revision  ;  many  subjects, 
notably  that  on  Gonorrhea,  have  been  practically  rewritten,  and  much  new  mate- 
rial has  been  added.  A  number  of  new  cuts  have  also  been  introduced,  besides 
a  series  of  beautiful  colored  lithographic  plates. 

American  Journal  of  Cutaneous  and  Genito-Urinary  Diseases 

"  It  is  a  plain,  practical,  and  up-to-date  manual  containing  just  the  kind  of  information 
that  physicians  need  to  cope  successfully  with  a  troublesome  class  of  diseases." 


SAUNDERS'    BOOKS   ON 


Briihl,  Politzer,  anl  Smith's 
Otology 


Atlas  and  Epitome  of  Otology.  By  GUSTAV  BRUHL,  M.  D.,  of 
Berlin,  with  the  collaboration  of  PROFESSOR  DR.  A.  POLITZER,  of 
Vienna.  Edited,  with  additions,  by  S.  MACCUEN  SMITH,  M.D.,  Pro- 
fessor of  Otology  in  the  Jefferson  Medical  College,  Philadelphia. 
With  244  colored  figures  on  39  lithographic  plates,  99  text  illustra- 
tions, and  292  pages  of  text.  Cloth,  $3.00  net.  In  Saunders'  Hand- 
Atlas  Series. 

INCLUDING  ANATOMY  AND  PHYSIOLOGY 

The  work  is  both  didactic  and  clinical  in  its  teaching.  A  special  feature  is 
the  very  complete  exposition  of  the  minute  anatomy  of  the  ear,  a  working  knowl- 
edge of  which  is  so  essential  to  an  intelligent  conception  of  the  science  of  otology. 
The  association  of  Professor  Politzer  and  the  use  of  so  many  valuable  specimens 
from  his  notably  rich  collection  especially  enhance  the  value  of  the  treatise.  The 
work  contains  everything  of  importance  in  the  elementary  study  of  otology. 

Clarence  J.  Blake.  M.  D., 

Professor  of  Otology  in  Harvard  University  Medical  School,  Boston. 

"  The  most  complete  work  of  its  kind  as  yet  published,  and  one  commending  itself  to  both 
the  student  and  the  teacher  in  the  character  and  scope  of  its  illustrations." 

Haab  anl  deSchweinitz's 

Operative  Ophthalmology 

Atlas  and  Epitome  of  Operative  Ophthalmology.  By  DR.  O. 
HAAB,  of  Zurich.  Edited,  with  additions,  by  G.  E.  DESCHWEINITZ, 
M.  D.,  Professor  of  Ophthalmology  in  the  University  of  Pennsylvania. 
With  30  colored  lithographic  plates,  1 54  text-cuts,  and  375  pages  of 
text.  In  Saunders"  Hand-Atlas  Series.  Cloth,  $3.50  net. 

RECENTLY   ISSUED 

Dr.  Haab's  Atlas  of  Operative  Ophthalmology  will  be  found  as  beautiful  and 
as  practical  as  his  two  former  atlases.  The  work  represents  the  author' s  thirty 
years'  experience  in  eye  work.  The  various  operative  interventions  are  described 
with  all  the  precision  and  clearness  that  such  an  experience  brings.  Recognizing 
the  fact  that  mere  verbal  descriptions  are  frequently  insufficient  to  give  a  clear 
idea  of  operative  procedures,  Dr.  Haab  has  taken  particular  care  to  illustrate 
plainly  the  different  parts  of  the  operations. 

Johns  Hopkins  Hospital  Bulletin 

"  The  descr  ptions  of  the  various  operit  ons  are  so  clear  and  full  that  the  volume  can  well 
hold  place  with  more  pretentious  text-books." 


DISEASES   OF   THE  EYE. 


tiaab  and  DeSchweinitz's 
External  Diseases  of  the  Eye 

Atlas  and  Epitome  of  External  Diseases  of  the  Eye.     By  DR.  O. 

HAAB,  of  Zurich.  Edited,  with  additions,  by  G.  E.  DESCHWEINITZ, 
M.  D.,  Professor  of  Ophthalmology,  University  of  Pennsylvania.  With 
98  colored  illustrations  on  48  lithographic  plates  and  232  pages  of 
text.  Cloth,  $3.00  net.  In  Saunders1  Hand-Atlas  Series. 

SECOND   REVISED   EDITION— RECENTLY   ISSUED 

Conditions  attending  diseases  of  the  external  eye,  which  are  often  so  complicated, 
have  probably  never  been  more  clearly  and  comprehensively  expounded  than  in 
the  forelying  work,  in  which  the  pictorial  most  happily  supplements  the  verbal 
description.  The  price  of  the  book  is  remarkably  low. 

The  Medical  Record,  New  York 

"  The  work  is  excellently  suited  to  the  student  of  ophthalmology  and  to  the  practising 
physician.     It  cannot  fail  to  attain  a  well-deserved  popularity." 

Haab  and  DeSchweinitzV 
Ophthalmoscopy 


Atlas  and  Epitome  of  Ophthalmoscopy  and  Ophthalmoscopic 
Diagnosis.  By  DR.  O.  HAAB,  of  Zurich.  From  the  Third  Revised 
and  Enlarged  German  Edition.  Edited,  with  additions,  by  G.  E. 
DESCHWEINITZ,  M.  D.,  Professor  of  Ophthalmology,  University  of 
Pennsylvania.  With  152  colored  lithographic  illustrations  and  85 
pages  of  text.  Cloth,  $3.00  net.  In  Saunders'  Hand-Atlas  Series. 

The  great  value  of  Prof.  Haab's  Atlas  of  Ophthalmoscopy  and  Ophthalmo- 
scopic Diagnosis  has  been  fully  established  and  entirely  justified  an  English 
translation.  Not  only  is  the  student  made  acquainted  with  carefully  prepared 
ophthalmoscopic  drawings  done  into  well-executed  lithographs  of  the  most  im- 
portant fundus  changes,  but,  in  many  instances,  plates  of  the  microscopic  lesions 
are  added.  The  whole  furnishes  a  manual  of  the  greatest  possible  service. 

The  Lancet,  London 

"We  recommend  it  as  a  work  that  should  be  in  the  ophthalmic  wards  or  in  the  library  of 
every  hospital  into  which  ophthalmic  cases  are  received." 


SAUNDERS"  BOOKS   ON 


Barton  and  Well/-' 
Medical  Thesaurus 

A  NEW  WORK— RECENTLY    ISSUED 


A  Thesaurus  of  Medical  Words  and  Phrases.  By  WILFRED  M. 
BARTON,  A.  M.,  Assistant  to  Professor  of  Materia  Medica  and  Thera- 
peutics, and  Lecturer  on  Pharmacy,  Georgetown  University,  Washing- 
ton, D.  C. ;  and  WALTER  A.  WELLS.  M.  D.,  Demonstrator  of  Laryn- 
gology, Georgetown  University,  Washington,  D.  C.  Handsome  I2mo 
of  534  pages.  Flexible  leather,  $2.50  net;  with  thumb  index,  $3.00 
net 

THE  ONLY   MEDICAL  THESAURUS   EVER   PUBLISHED 

This  work  is  unique  in  that  it  is  the  only  Medical  Thesaurus  ever  published. 
Instead  of  supplying  the  meaning  to  given  words,  as  an  ordinary  dictionary  does, 
it  reverses  the  process,  and  when  the  meaning  or  idea  is  in  the  mind  it  endeavors 
to  supply  the  fitting  term  or  phrase  to  express  that  idea.  This  Thesaurus  will  be 
of  service  to  all  persons  who  are  called  upon  to  state  or  explain  any  subject  in  the 
technical  language  of  medicine. 

Boston  Medical  and  Surgical  Journal 

"  We  can  easily  see  the  value  of  such  a  book,  and  can  certainly  recommend  it  to  our 
readers." 

Saxe's  Urinalysis 


Examination  of  the  Urine.  By  G.  A.  DE  SANTOS  SAXE,  M.  D., 
Pathologist  to  Columbus  Hospital,  New  York  City.  I2mo  of  391 
pages,  fully  illustrated.  Flexible  leather,  $1.50  net. 

RECENTLY  ISSUED 

This  work  is  intended  as  an  aid  in   diagnosis,   by  interpreting  the  clinical 
significance  of  the  chemic  and  microscopic   urinary  findings. 

Francis  Carter  Wood.    M.  D., 

Adjunct  Professor  of  Clinical  Pathology,   Columbia   University. 

"It  seems  to  me  to  be  one  of  the  best  of  the  smaller  works  on  this  subject ;  it  is  indeed,  better 
than  a  good  many  of  the  larger  ones." 


NOSE,    THROAT,  AND   EAR. 


Cradle's 
Nose,  Pharynx,  and  Ear 

Diseases  of  the  Nose,  Pharynx,  and  Ear.  By  HENRY  GRADLE, 
M.  D.,  Professor  of  Ophthalmology  and  Otology,  Northwestern  Uni- 
versity Medical  School,  Chicago.  Handsome  octavo  of  547  pages, 
illustrated,  including  two  full-page  plates  in  colors.  Cloth,  $3.50  net. 

INCLUDING  TOPOGRAPHIC  ANATOMY 

This  volume  presents  diseases  of  the  Nose,  Pharynx,  and  Ear  as  the  author 
has  seen  them  during  an  experience  of  nearly  twenty-five  years.  In  it  are 
answered  in  detail  those  questions  regarding  the  course  and  outcome  of  diseases 
which  cause  the  less  experienced  observer  the  most  anxiety  in  an  individual  case. 
Topographic  anatomy  has  been  accorded  liberal  space. 

Pennsylvania  Medical  Journal 

"This  is  the  most  practical  volume  on  the  nose,  pharynx,  and  ear  that  has  appeared 
recently.  ...  It  is  exactly  what  the  less  experienced  observer  needs,  as  it  avoids  the  confusion 
incident  to  a  categorical  statement  of  everybody's  opinion." 

Kyle's 
Diseases  of  Nose  and  Throat 


Diseases  of  the  Nose  and  Throat.  By  D.  BRADEN  KYLE,  M.  D., 
Professor  of  Laryngology  in  the  Jefferson  Medical  College,  Phila- 
delphia ;  Consulting  Laryngologist,  Rhinologist,  and  Otologist,  St. 
Agnes'  Hospital.  Octavo,  669  pages;  over  184  illustrations,  and  26 
lithographic  plates  in  colors.  Cloth,  $4.00  net. 

RECENTLY   ISSUED— THIRD   REVISED   EDITION 

Three  large  editions  of  this  excellent  work  fully  testify  to  its  practical 
value.  In  this  edition  the  author  has  revised  the  text  thoroughly,  bringing 
it  absolutely  down  to  date.  With  the  practical  purpose  of  the  book  in  mind,  ex- 
tended consideration  has  been  given  to  treatment,  each  disease  being  considered  in 
full,  and  definite  courses  being  laid  down  to  meet  special  conditions  and  symptoms. 

Dudley  S.  Reynolds,  M.  D., 

Formerly  Professor  of  Ophthalmology  and  Otology,  Hospital  College  of  Medicine,  Louisville. 
"  It  is  an  important  addition  to  the  text-books  now  in  use,  and  is  better  adapted  to  the  uses 
of  the  student  than  any  other  work  with  which  I  am  familiar.     I  shall  be  pleased  to  commend 
Dr.  Kvle's  work  as  the  best  text-book." 


io  SAUNDERS'  BOOKS   ON 

Griinwald  anl  Grayson's 
Diseases  of  the  Larynx 

Atlas  and  Epitome  of  Diseases  of  the  Larynx.  By  DR.  L.  GRUN- 
WALD,  of  Munich.  Edited,  with  additions,  by  CHARLES  P.  &RAYSON, 
M.  D.,  Clinical  Professor  of  Laryngology  and  Rhinology,  University 
of  Pennsylvania.  With  107  colored  figures  on  44  plates,  25  text-cuts, 
and  103  pages  of  text.  Cloth,  #2.50  net.  In  Saundcrs  Hand-Atlas 
Series. 

British  Medical  Journal 

"  Excels  everything  we  have  hitherto  seen  in  the  way  of  colored  illustrations  of  diseases  of 
the  larynx.  .  .  .  Not  only  valuable  for  the  teaching  of  laryngology,  it  will  prove  of  the  greatest 
help  to  those  who  are  perfecting  themselves  by  private  study." 

American  Text-Book  of 

Genito-Urinary,  Syphilis,  Skin 

American  Text-book  of  Genito-Urinary  Diseases,  Syphilis,  and 
Diseases  of  the  Skin.  Edited  by  L.  BOLTON  BANGS,  M.  D.,  late  Prof, 
of  Genito-Urinary  Surgery,  University  and  Bellevue  Hospital  Medical 
College.  New  York;  and  W.  A.  HARDAWAY,  M.  D.,  Professor  of  Diseases 
of  the  Skin,  Missouri  Medical  College.  Imperial  octavo,  1229  pages, 
with  300  engravings,  20  colored  plates.  Cloth,  $7.00  net 

Journal  of  the  American  Medical  Association 

"  This  voluminous  work  is  thoroughly  up-to-date,  and  the  chapters  on  genito-urinary  dis- 
eases are  especially  valuable.  The  illustrations  are  fine  and  are  mostly  original.  The  section 
on  dermatology  is  concise  and  in  every  way  admirable." 

SennV 

Genito-Urinary   Tuberculosis 

Tuberculosis  of  the  Genito-Urinary  Organs,  Male  and  Female. 
By  N.  SENN,  M.D.,  PH.  D.,  LL.D.,  Professor  of  Surgery  in  Rush  Med- 
ical College.  Octavo  of  317  pages,  illustrated.  Cloth,  $3.00  net. 

British  Medical  Journal 

"  The  book  will  well  repay  perusal.  It  is  the  final  word,  as  our  knowledge  stands,  upon 
the  diseases  of  which  it  treats,  and  will  add  to  the  reputation  of  its  distinguished  author." 


DISEASES   OF  THE  SKIN.  n 

Mracek  arw  Stelwagon's 
Diseases  of  the  Skin 

Atlas  and  Epitome  of  Diseases  of  the  Skin.  By  PROF.  DR.  FRANZ 
MRACEK,  of  Vienna.  Edited,  with  additions,  by  HENRY  W.  STELWAGON, 
M.  D.,  Professor  of  Dermatology  in  the  Jefferson  Medical  College, 
Philadelphia.  With  77  colored  plates,  50  half-tone  illustrations,  and 
280  pages  of  text.  In  Saunders'  Hand-Atlas  Series.  Clo.,  $4.  oo  net. 

RECENTLY   ISSUED— NEW  (2nd)  EDITION 

This  volume,  the  outcome  of  years  of  scientific  and  artistic  work,  contains, 
together  with  colored  plates  of  unusual  beauty,  numerous  illustrations  in  black, 
and  a  text  comprehending  the  entire  field  of  dermatology.  The  illustrations  are 
all  original  and  prepared  from  actual  cases  in  Mracek' s  clinic,  and  the  execution 
of  the  plates  is  superior  to  that  of  any,  even  the  most  expensive,  dermatologic 
atlas  hitherto  published. 

American  Journal  of  the  Medical  Sciences 

"  The  advantages  which  we  see  in  this  book  and  which  recommend  it  to  our  minds  are : 
First,  its  handiness ;  secondly,  the  plates,  which  are  excellent  as  regards  drawing,  color,  and  the 
diagnostic  points  which  they  bring  out." 

Mracek  aric  Bangs' 
Syphilis  and  Venereal 

Atlas    and    Epitome   of    Syphilis    and    the    Venereal    Diseases. 

By  PROF.  DR.  FRANZ  MRACEK,  of  Vienna.  Edited,  with  additions,  by 
L.  BOLTON  BANGS,  M.  D.,  late  Prof,  of  Genito-Urinary  Surgery,  Univer- 
sity and  Bellevue  Hospital  Medical  College,  New  York.  With  71 
colored  plates  and  122  pages  of  text.  Cloth,  $3.50  net.  In  Saunders' 
Hand-Atlas  Series. 

CONTAINING   71   COLORED   PLATES 

According  to  the  unanimous  opinion  of  numerous  authorities,  to  whom  the 
original  illustrations  of  this  book  were  presented,  they  surpass  in  beauty  anything 
of  the  kind  that  has  been  produced  in  this  field,  not  only  in  Germany,  but 
throughout  the  literature  of  the  world. 

Robert  L.  Dickinson,  M.  D., 

Art  Editor  of  "  The  American  Text-Book  of  Obstetrics." 

"  The  book  that  appeals  instantly  to  me  for  the  strikingly  successful,  valuable,  and  graphic 
character  of  its  illustrations  is  the  '  Atlas  of  Syphilis  and  the  Venereal  Diseases.'  I  know  of 
nothing  in  this  country  that  can  compare  with  it." 


12  SAUNDERS'  BOOKS   ON 


A  Text-Book  of  Medical  Chemistry  and  Toxicology.  By  JAMES 
W.  HOLLAND,  M.  D.,  Professor  of  Medical  Chemistry  and  Toxicology, 
and  Dean,  Jefferson  Medical  College,  Philadelphia.  Octavo  of  592 
pages,  fully  illustrated.  Cloth,  $3.00  net. 

RECENTLY   ISSUED 

Dr.  Holland's  work  is  an  entirely  new  one,  and  is  based  on  his  thirty-five 
years'  practical  experience  in  teaching  chemistry  and  medicine.  Recognizing 
that  to  understand  physiologic  chemistry,  students  must  first  be  informed  upon 
points  not  referred  to  in  most  medical  text-books,  the  author  has  included  in  his 
work  the  latest  views  of  equilibrium  of  equations,  mass  action,  cryoscopy,  os- 
motic pressure,  cV.ssociation  of  salts  into  ions,  effects  of  ionization  upon  electric 
conductivity,  and  the  relationship  between  purin  bodies,  uric  acid,  and  urea. 
More  space  is  given  to  toxicology  than  in  any  other  text-book  on  chemistry. 

American  Medicine 

"  Its  statements  are  clear  and  terse  ;  its  illustrations  well  chosen  ;  its  development  logical, 
systematic,  and  comparatively  easy  to  follow.  .  .  .  We  heartily  commend  the  work." 

Grtinwald  anl  Newcomb's 
Mouth,  Pharynx,  and  Nose 

Atlas  and  Epitome  of  Diseases  of  the  Mouth,  Pharynx,  and 
Nose.  By  DR.  L.  GRUNWALD,  of  Munich.  From  the  Second  Reinsed 
and  Enlarged  German  Edition.  Edited,  with  additions,  by  JAMES  E. 
NEWCOMB,  M.  D.,  Instructor  in  Laryngology,  Cornell  University  Medical 
School.  With  1  02  illustrations  on  42  colored  lithographic  plates,  41 
text-cuts,  and  219  pages  of  text.  Cloth,  $3.00  net.  In  Saunders' 
Hand-Atlas  Series. 

INCLUDING  ANATOMY  AND  PHYSIOLOGY 

In  designing  this  atlas  the  needs  of  both  student  and  practitioner  were  kept 
constantly  in  mind,  and  as  far  as  possible  typical  cases  of  the  various  diseases 
were  selected.  The  illustrations  are  described  in  the  text  in  exactly  the  same  way 
as  a  practised  examiner  would  demonstrate  the  objective  findings  to  his  class. 
The  illustrations  themselves  are  numerous  and  exceedingly  well  executed.  The 
editor  has  incorporated  his  own  valuable  experience,  and  has  also  included  exten- 
sive notes  on  the  use  of  the  active  principle  of  the  suprarenal  bodies. 

American  Medicine 

"  Its  conciseness  without  sacrifice  of  clearness  and  thoroughness,  as  well  as  the  excellence 
of  text  and  illustrations,  are  commendable." 


EYE,  EAR,  NOSE,  AND    THROAT.  13 

Jackson  on  the  Eye 

A  Manual  of  the  Diagnosis  and  Treatment  of  Diseases  of  the  Eye. 

By  EDWARD  JACKSON,  A.  M.,  M.  D.,  Emeritus  Professor  of  Diseases  of 
the  Eye  in  the  Philadelphia  Polyclinic.  I2mo  volume  of  535  pages, 
with  178  beautiful  illustrations,  mostly  from  drawings  by  the  author. 
Cloth,  $2.50  net. 

The  Medical  Record,  New  York 

"  It  is  truly  an  admirable  work.  .  .  .  Written  in  a  clear,  concise  manner,  it  bears  evidence 
of  the  author's  comprehensive  grasp  of  the  subject.  The  term  '  multum  in  parvo  '  is  an  appro- 
priate one  to  apply  to  this  work.  It  will  prove  of  value  to  all  who  are  interested  in  this  branch 
of  medicine." 

Grant  on  the 
Face,  Mouth,  and  Jaws 

A  Text=Book  of  the  Surgical  Principles  and  Surgical  Diseases  of 
the  Face,  Mouth,  and  Jaws.  For  Dental  Students.  By  H.  HORACE 
GRANT,  A.  M.,  M.  D.,  Professor  of  Surgery  and  of  Clinical  Surgery, 
Hospital  College  of  Medicine,  Louisville.  Octavo  of  231  pages,  with 
68  illustrations.  Cloth,  $2.50  net. 

Annals  of  Surgery 

"  The  book  is  well  illustrated,  the  text  is  clear,  and  on  the  whole  it  serves  well  for  the 
purpose  for  which  it  is  intended." 

Friedrich  arid  Curtis' 
Nose,  Larynx,  and  Ear 

Rhinology,  Laryngology,  and  Otology,  and  Their  Significance  in 
General  Medicine.  By  DR.  E.  P.  FRIEDRICH,  of  Leipzig.  Edited  by 
H.  HOLBROOK  CURTIS,  M.  D.,  Consulting  Surgeon  to  the  New  York 
Nose  and  Throat  Hospital.  Octavo  volume  of  350  pages.  Cloth, 
$2.50  net. 

Boston  Medical  and  Surgical  Journal 

"  This  task  he  has  performed  admirably,  and  has  given  both  to  the  general  practitioner  and 
to  the  specialist  a  book  for  collateral  reference  which  is  modern,  clear,  and  complete." 


14  SAUNDERS'    BOOKS   ON 

Ogden  on  the  Urine 


Clinical  Examination  of  Urine  and  Urinary  Diagnosis.  A  Clinical 
Guide  for  the  Use  of  Practitioners  and  Students  of  Medicine  and  Sur- 
gery. By  J.  BERGEN  OGDEN,  M.  D.,  Late  Instructor  in  Chemistry, 
Harvard  University  Medical  School ;  Formerly  Assistant  in  Clinical 
Pathology,  Boston  City  Hospital.  Octavo,  418  pages,  54  illustrations, 
and  a  number  of  colored  plates.  Cloth,  $3.00  net. 

SECOND  REVISED  EDITION— RECENTLY  ISSUED 

In  this  edition  the  work  has  been  brought  absolutely  down  to  the  present  day. 
Important  changes  have  been  made  in  connection  with  the  determination  of  Urea, 
Uric  Acid,  and  Total  Nitrogen  ;  and  the  subjects  of  Cryoscopy  and  Beta-Ox y butyric 
Acid  have  been  given  a  place.  Special  attention  has  been  paid  to  diagnosis  by 
the  character  of  the  urine,  the  diagnosis  of  diseases  of  the  kidneys  and  urinary 
passages  ;  an  enumeration  of  the  prominent  clinical  symptoms  of  each  disease  ; 
and  the  peculiarities  of  the  urine  in  certain  general  diseases. 

The  Lancet,  London 

"  We  consider  this  manual  to  have  been  well  compiled ;  and  the  author's  own  experience, 
so  clearly  stated,  renders  the  volume  a  useful  one  both  for  study  and  reference." 

Vecki's  Sexual  Impotence 


The  Pathology  and  Treatment  of  Sexual  Impotence.  By  VICTOR 
G.  VECKI,  M.  D.  From  the  Second  Revised  and  Enlarged  German 
Edition.  I2mo  volume  of  329  pages.  Cloth,  $2.00  net. 

THIRD   EDITION,  REVISED   AND   ENLARGED 

The  subject  of  impotence  has  but  seldom  been  treated  in  this  country  in  the 
truly  scientific  spirit  that  its  pre-eminent  importance  deserves,  and  this  volume  will 
come  to  many  as  a  revelation  of  the  possibilities  of  therapeutics  in  this  important 
field.  The  reading  part  of  the  English-speaking  medical  profession  has  passed 
judgment  on  this  monograph.  The  whole  subject  of  sexual  impotence  and  its 
treatment  is  discussed  by  the  author  in  an  exhaustive  and  thoroughly  scientific 
manner.  In  this  edition  the  book  has  been  thoroughly  revised,  and  new  matter 
has  been  added,  especially  to  the  portion  dealing  with  treatment. 

Johns  Hopkins  Hospital  Bulletin 

"  A  scientific  treatise  upon  an  important  and  much  neglected  subject.  .  .  .  The  treatment 
of  impotence  in  general  and  of  sexual  neurasthenia  is  discriminating  and  judicious." 


CHEMISTRY,  SKIN,  AND   VENEREAL   DISEASES.  15 

A  •  rfc        t      j_    TV*    A.*  Fourth  Edition,  Revised 

American  Pocket  Dictionary  Recently  issued 

THE  AMERICAN  POCKET  MEDICAL  DICTIONARY.  Edited  by  W.  A. 
NEWMAN  DORLAND,  M.  D.,  Assistant  Obstetrician  to  the  Hospital 
of  the  University  of  Pennsylvania.  Containing  the  pronunciation 
and  definition  of  the  principal  words  used  in  medicine  and  kindred 
sciences.  Flexible  leather,  with  gold  edges,  $1.00  net  ;  with  thumb 
index,  #1.25  net. 
James  W.  Holland,  M.  D., 

Professor  of  Medical  Chemistry  and  Toxicology,  and  Dean,  Jefferson  Medical  College, 
Philadelphia, 

"  I  am  struck  at  once  with  admiration  at  the  compact  size  and  attractive  exterior.     I 
can  recommend  it  to  our  students  without  reserve." 

Stelwagon's  Essentials  of  Skin  Sit£^hSdm 

ESSENTIALS  OF  DISEASES  OF  THE  SKIN.  By  HENRY  W.  STEL- 
WAGON,  M.  D.,  PH.D.,  Professor  of  Dermatology  in  the  Jeffer- 
son Medical  Colle^o,  Philadelphia.  Post-octavo  of  276  pages, 
with  72  text-illustrations  and  8  plates.  Cloth,  $1.00  net.  In 
Saunders1  Question-  Compend  Series. 
The  Medical  News 

"  In  line  with  our  present  knowledge  of  diseases  of  the  skin.  .  .  .  Continues  to  main- 
tain the  high  standard  of  excellence  for  which  these  question  compends  have  been  noted." 


Wolffs  Medical  Chemistry 

ESSENTIALS  OF  MEDICAL  CHEMISTRY,  ORGANIC  AND  INORGANIC. 
Containing  also  Questions  on  Medical  Physics,  Chemical  Physiol- 
ogy, Analytical  Processes,  Urinalysis,  and  Toxicology.  By  LAW- 
RENCE WOLFF,  M.  D.,  Late  Demonstrator  of  Chemistry,  Jefferson 
Medical  College.  Revised  by  SMITH  ELY  JELLIFFE,  M.  D.,  PH.D., 
Professor  of  Pharmacognosy,  College  of  Pharmacy  of  the  City  of 
New  York.  Post-octavo  of  222  pages.  Cloth,  $1.00  net.  In 
Saunders'  Question-  Compend  Series. 
New  York  Medical  Journal 

"  The  author's  careful  and  well-studied  selection  of  the  necessary  requirements  of  the 
student  has  enabled  him  to  furnish  a  valuable  aid  to  the  student." 

Martin's  Minor  Surgery,  Bandaging,  and  the  Venereal 

Diseases  Second  Edition.  Revised 

ESSENTIALS  OF  MINOR  SURGERY,  BANDAGING,  AND  VENEREAL 
DISEASES.  By  EDWARD  MARTIN,  A.  M.,  M.  D.,  Professor  of  Clin- 
ical Surgery,  University  of  Pennsylvania,  etc.  Post-octavo,  166 
pages,  with  78  illustrations.  Cloth,  $1.00  net.  In  Saunders' 
Question-  Compend  Series. 
The  Medical  News 

"The  best  condensation  of  the  subjects  of  which  it  treats  yet  placed  before  the  pro- 
fession." 


16  URINE,  EYE,  EAR,  NOSE,  AND    THROAT. 

Wolfs  Examination  of  Urine 

A  LABORATORY  HANDBOOK  OF  PHYSIOLOGIC  CHEMISTRY  AND 
URINE-EXAMINATION.  By  CHARLES  G.  L.  WOLF,  M.  D.,  Instructor  in 
Physiologic  Chemistry,  Cornell  University  Medical  College,  New 
York.  I2mo  volume  of  204  pages,  fully  illustrated.  Cloth,  $1.25  net. 
British  Medical  Journal 

"  The  methods  of  examining  the  urine  are  very  fully  described,  and  there  are  at  the 
end  of  the  book  some  extensive  tables  drawn  up  to  assist  in  urinary  diagnosis." 

Jackson's  Essentials  of  Eye  Third  Revised  edition 

ESSENTIALS  OF  REFRACTION  AND  OF  DISEASES  OF  THE  EYE.  By 
EDWARD  JACKSON,  A.  M.,  M.  D.,  Emeritus  Professor  of  Diseases  of 
the  Eye,  Philadelphia  Polyclinic.  Post-octavo  of  261  pages,  82  illus- 
trations. Cloth,  $1.00  net.  ///  Saunders'  Question- Compend  Series. 
Johns  Hopkins  Hospital  Bulletin 

"  The  entire  ground  is  covered,  and  the  points  that  most  need  careful  elucidation 
are  made  clear  and  easy." 

Gleason's  Nose  and  Throat  Third  Edition,  Revised 

ESSENTIALS  OF  DISEASES  OF  THE  NOSE  AND  THROAT.  By  E.  B. 
GLEASON,  S.  B.,  M.  D.,  Clinical  Professor  of  Otology,  Medico- 
Chirurgical  College,  Philadelphia,  etc.  Post-octavo,  24 1  pages,  112 
illustrations.  Cloth,  $1.00  net.  /;/  Saunders'  Question  Commends. 
The  Lancet,  London 

"  The  careful  description  which  is  given  of  the  various  procedures  would  be  sufficient 
to  enable  most  people  of  average  intelligence  and  of  slight  anatomical  knowledge  to 
make  a  very  good  attempt  at  laryngoscopy." 

Gleason's  Diseases  of  the  Ear  Third  Edition,  Revised 

ESSENTIALS  OF  DISEASES  OF  THE  EAR.     By  E.  B.  GLEASON,  S.  B., 
M.  D.,  Clinical  Professor  of  Otology,  Medico-Chirurgical  College, 
Phila.,  etc.     Post-octavo  volume  of  214  pages,  with   114  illustra- 
tions.    Cloth,  $  i. oo  net.     In  Saunders'  Question- Compend  Series. 
Bristol  Medico-Chirurgical  Journal 

"We  know  of  no  other  small  work  on  ear  diseases  to  compare  with  this,  either  in 
freshness  of  style  or  completeness  of  information." 

\Vilcox  on  Genito- Urinary  and  Venereal  Diseases    ,SJJuued 

ESSENTIALS  OF  GENITO-URINARY  AND  VENEREAL  DISEASES.  By 
STARLING  S.  WILCOX,  M.  D.,  Professor  of  Genito-Urinary  Diseases 
and  Syphilology,  Starling  Medical  College,  Columbus,  Ohio.  I2mo 
of  313  pages,  illustrated.  Cloth,  $I.OO  net.  Saunders'  Co)npi-nds. 

Stevenson's  Photoscopy  j™t  Ready 

PHOTOSCOPY.  (Skiascopy  or  Retinoscopy)  By  MARK  D.  STEV- 
ENSON, M.  D.,  Ophthalmic  Surgeon  to  the  Akron  City  Hospital. 
I2mo  of  200  pages,  illustrated. 

Dr.  Stevenson's  work  fully  and  clearly  explains  the  use  of  this  objective  test  and 
elucidates  the  reasons  of  the  various  phenomena  observed.  The  illustrations  have  been 
drawn  with  special  attention  to  their  practical  usefulness. 


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